blocks|key|1520752|text|Mac是Unix，Objective-C是C超集，所以你可以只使用<stdio.h>的老式fopen和fgets。它肯定会起作用。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1520753|[NSString+stringWithUTF8String:buf]会将C字符串转换为NSString。还有一些方法可以用其他编码创建字符串，也可以在不复制的情况下创建字符串。|1520754|entityMap^0|X|9|19|5|1F|5|0|0|Z|18|8|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]|$9|O|A|P|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Q|8|@$9|R|A|S|B|C]|$9|T|A|U|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|I|$]]

Mac OS X is Unix, Objective-C is C superset, so you can just use old-school <code>fopen</code> and <code>fgets</code> from <code>&lt;stdio.h&gt;</code>. It's guaranteed to work.

<code>[NSString stringWithUTF8String:buf]</code> will convert C string to <code>NSString</code>. There are also methods for creating strings in other encodings and creating without copying.

blocks|key|1305662|text|您可以使用NSInputStream，它有一个基本的文件流实现。您可以将字节读入缓冲区(read:maxLength:方法)。您必须自己扫描缓冲区中的换行符。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1305663|entityMap^0|5|D|18|F|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|M|8|@]|D|@]|E|$]]]|G|$]]

You can use <code>NSInputStream</code> which has a basic implementation for file streams. You can read bytes into a buffer (<code>read:maxLength:</code> method). You have to scan the buffer for newlines yourself.

blocks|key|1306091|text|这些答案中的许多都是很长的代码块，或者它们在整个文件中读取。我喜欢使用c方法来完成这项任务。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1306092|FILE*+file+=+fopen("path+to+my+file",+"r");

size_t+length;
char+*cLine+=+fgetln(file,&length);

while+(length>0)+{
++++char+str[length%2B1];
++++strncpy(str,+cLine,+length);
++++str[length]+=+'\0';

++++NSString+*line+=+[NSString+stringWithFormat:@"%25s",str];++++++++
++++%25+Do+what+you+want+here.

++++cLine+=+fgetln(file,&length);
}|code-block|syntax|javascript|1306093|注意，fgetln不会保留换行符。另外，我们%2B1字符串的长度，因为我们想为空终止腾出空间。|1306094|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

A lot of these answers are long chunks of code or they read in the entire file. I like to use the c methods for this very task.

<pre><code>FILE* file = fopen("path to my file", "r");

size_t length;
char *cLine = fgetln(file,&amp;length);

while (length&gt;0) {
 char str[length+1];
 strncpy(str, cLine, length);
 str[length] = '\0';

 NSString *line = [NSString stringWithFormat:@"%s",str]; 
 % Do what you want here.

 cLine = fgetln(file,&amp;length);
}
</code></pre>

Note that fgetln will not keep your newline character. Also, We +1 the length of the str because we want to make space for the NULL termination.

blocks|key|1305857|text|正如@porneL所说，C+api非常方便。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1305858|NSString*+fileRoot+=+[[NSBundle+mainBundle]+pathForResource:@"record"+ofType:@"txt"];
FILE+*file+=+fopen([fileRoot+UTF8String],+"r");
char+buffer[256];
while+(fgets(buffer,+256,+file)+!=+NULL){
++++NSString*+result+=+[NSString+stringWithUTF8String:buffer];
++++NSLog(@"%25@",result);
}|code-block|syntax|javascript|1305859|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Just like @porneL said, the C api is very handy.

<pre><code>NSString* fileRoot = [[NSBundle mainBundle] pathForResource:@"record" ofType:@"txt"];
FILE *file = fopen([fileRoot UTF8String], "r");
char buffer[256];
while (fgets(buffer, 256, file) != NULL){
 NSString* result = [NSString stringWithUTF8String:buffer];
 NSLog(@"%@",result);
}
</code></pre>

blocks|key|1305901|text|正如其他人回答的那样，NSInputStream和NSFileHandle都是很好的选择，但也可以通过NSData和内存映射以相当紧凑的方式完成：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1305902|BRLineReader.h|1305903|#import+<Foundation/Foundation.h>

@interface+BRLineReader+:+NSObject

@property+(readonly,+nonatomic)+NSData+*data;
@property+(readonly,+nonatomic)+NSUInteger+linesRead;
@property+(strong,+nonatomic)+NSCharacterSet+*lineTrimCharacters;
@property+(readonly,+nonatomic)+NSStringEncoding+stringEncoding;

-+(instancetype)initWithFile:(NSString+*)filePath+encoding:(NSStringEncoding)encoding;
-+(instancetype)initWithData:(NSData+*)data+encoding:(NSStringEncoding)encoding;
-+(NSString+*)readLine;
-+(NSString+*)readTrimmedLine;
-+(void)setLineSearchPosition:(NSUInteger)position;

@end|code-block|syntax|javascript|1305904|BRLineReader.m|1305905|#import+"BRLineReader.h"

static+unsigned+char+const+BRLineReaderDelimiter+=+'\n';

@implementation+BRLineReader
{
++++NSRange+_lastRange;
}

-+(instancetype)initWithFile:(NSString+*)filePath+encoding:(NSStringEncoding)encoding
{
++++self+=+[super+init];
++++if+(self)+{
++++++++NSError+*error+=+nil;
++++++++_data+=+[NSData+dataWithContentsOfFile:filePath+options:NSDataReadingMappedAlways+error:&error];
++++++++if+(!_data)+{
++++++++++++NSLog(@"%25@",+[error+localizedDescription]);
++++++++}
++++++++_stringEncoding+=+encoding;
++++++++_lineTrimCharacters+=+[NSCharacterSet+whitespaceAndNewlineCharacterSet];
++++}

++++return+self;
}

-+(instancetype)initWithData:(NSData+*)data+encoding:(NSStringEncoding)encoding
{
++++self+=+[super+init];
++++if+(self)+{
++++++++_data+=+data;
++++++++_stringEncoding+=+encoding;
++++++++_lineTrimCharacters+=+[NSCharacterSet+whitespaceAndNewlineCharacterSet];
++++}

++++return+self;
}

-+(NSString+*)readLine
{
++++NSUInteger+dataLength+=+[_data+length];
++++NSUInteger+beginPos+=+_lastRange.location+%2B+_lastRange.length;
++++NSUInteger+endPos+=+0;
++++if+(beginPos+==+dataLength)+{
++++++++//+End+of+file
++++++++return+nil;
++++}

++++unsigned+char+*buffer+=+(unsigned+char+*)[_data+bytes];
++++for+(NSUInteger+i+=+beginPos;+i+<+dataLength;+i%2B%2B)+{
++++++++endPos+=+i;
++++++++if+(buffer[i]+==+BRLineReaderDelimiter)+break;
++++}

++++//+End+of+line+found
++++_lastRange+=+NSMakeRange(beginPos,+endPos+-+beginPos+%2B+1);
++++NSData+*lineData+=+[_data+subdataWithRange:_lastRange];
++++NSString+*line+=+[[NSString+alloc]+initWithData:lineData+encoding:_stringEncoding];
++++_linesRead%2B%2B;

++++return+line;
}

-+(NSString+*)readTrimmedLine
{
++++return+[[self+readLine]+stringByTrimmingCharactersInSet:_lineTrimCharacters];
}

-+(void)setLineSearchPosition:(NSUInteger)position
{
++++_lastRange+=+NSMakeRange(position,+0);
++++_linesRead+=+0;
}

@end|1305906|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

As others have answered both NSInputStream and NSFileHandle are fine options, but it can also be done in a fairly compact way with NSData and memory mapping:

BRLineReader.h

<pre><code>#import &lt;Foundation/Foundation.h&gt;

@interface BRLineReader : NSObject

@property (readonly, nonatomic) NSData *data;
@property (readonly, nonatomic) NSUInteger linesRead;
@property (strong, nonatomic) NSCharacterSet *lineTrimCharacters;
@property (readonly, nonatomic) NSStringEncoding stringEncoding;

- (instancetype)initWithFile:(NSString *)filePath encoding:(NSStringEncoding)encoding;
- (instancetype)initWithData:(NSData *)data encoding:(NSStringEncoding)encoding;
- (NSString *)readLine;
- (NSString *)readTrimmedLine;
- (void)setLineSearchPosition:(NSUInteger)position;

@end
</code></pre>

BRLineReader.m

<pre><code>#import "BRLineReader.h"

static unsigned char const BRLineReaderDelimiter = '\n';

@implementation BRLineReader
{
 NSRange _lastRange;
}

- (instancetype)initWithFile:(NSString *)filePath encoding:(NSStringEncoding)encoding
{
 self = [super init];
 if (self) {
 NSError *error = nil;
 _data = [NSData dataWithContentsOfFile:filePath options:NSDataReadingMappedAlways error:&amp;error];
 if (!_data) {
 NSLog(@"%@", [error localizedDescription]);
 }
 _stringEncoding = encoding;
 _lineTrimCharacters = [NSCharacterSet whitespaceAndNewlineCharacterSet];
 }

 return self;
}

- (instancetype)initWithData:(NSData *)data encoding:(NSStringEncoding)encoding
{
 self = [super init];
 if (self) {
 _data = data;
 _stringEncoding = encoding;
 _lineTrimCharacters = [NSCharacterSet whitespaceAndNewlineCharacterSet];
 }

 return self;
}

- (NSString *)readLine
{
 NSUInteger dataLength = [_data length];
 NSUInteger beginPos = _lastRange.location + _lastRange.length;
 NSUInteger endPos = 0;
 if (beginPos == dataLength) {
 // End of file
 return nil;
 }

 unsigned char *buffer = (unsigned char *)[_data bytes];
 for (NSUInteger i = beginPos; i &lt; dataLength; i++) {
 endPos = i;
 if (buffer[i] == BRLineReaderDelimiter) break;
 }

 // End of line found
 _lastRange = NSMakeRange(beginPos, endPos - beginPos + 1);
 NSData *lineData = [_data subdataWithRange:_lastRange];
 NSString *line = [[NSString alloc] initWithData:lineData encoding:_stringEncoding];
 _linesRead++;

 return line;
}

- (NSString *)readTrimmedLine
{
 return [[self readLine] stringByTrimmingCharactersInSet:_lineTrimCharacters];
}

- (void)setLineSearchPosition:(NSUInteger)position
{
 _lastRange = NSMakeRange(position, 0);
 _linesRead = 0;
}

@end
</code></pre>

blocks|key|1305609|text|这个答案不是ObjC，而是C。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1305610|既然ObjC是基于“C”的，为什么不使用fgets呢？|1305611|是的，我相信ObjC有它自己的方法--我只是还不够熟练，不知道它是什么:)|1305612|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

This answer is NOT ObjC but C.

Since ObjC is 'C' based, why not use fgets?

And yes, I'm sure ObjC has it's own method - I'm just not proficient enough yet to know what it is :)

blocks|key|1305945|text|根据@Adam+Rosenfield的回答，fscanf的格式化字符串将更改如下：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1305946|"%254095[%5E\r\n]%25n%25*[\n\r]"|code-block|syntax|javascript|1305947|它可以在osx，linux，windows下运行。|1305948|entityMap^0|M|6|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|N|$]]

from @Adam Rosenfield's answer, the formatting string of <code>fscanf</code> would be changed like below:

<pre><code>"%4095[^\r\n]%n%*[\n\r]"
</code></pre>

it will work in osx, linux, windows line endings.

blocks|key|1521005|text|使用类别或扩展让我们的生活变得更容易。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1521006|extension+String+{

++++func+lines()+->+[String]+{
++++++++var+lines+=+[String]()
++++++++self.enumerateLines+{+(line,+stop)+->+()+in
++++++++++++lines.append(line)
++++++++}
++++++++return+lines
++++}

}

//+then
for+line+in+string.lines()+{
++++//+do+the+right+thing
}|code-block|syntax|javascript|1521007|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Using category or extension to make our life a bit easier.

<pre><code>extension String {

 func lines() -&gt; [String] {
 var lines = [String]()
 self.enumerateLines { (line, stop) -&gt; () in
 lines.append(line)
 }
 return lines
 }

}

// then
for line in string.lines() {
 // do the right thing
}
</code></pre>

blocks|key|1306028|text|我发现@lukaswelte的响应和Dave+DeLong的代码非常有帮助。我一直在寻找这个问题的解决方案，但我需要通过\r\n而不仅仅是\n来解析大文件。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1306029|所编写的代码包含一个错误，如果通过一个以上的字符进行解析。我已经修改了代码，如下所示。|1306030|.h文件：|1306031|#import+<Foundation/Foundation.h>

@interface+FileChunkReader+:+NSObject+{
++++NSString+*+filePath;

++++NSFileHandle+*+fileHandle;
++++unsigned+long+long+currentOffset;
++++unsigned+long+long+totalFileLength;

++++NSString+*+lineDelimiter;
++++NSUInteger+chunkSize;
}

@property+(nonatomic,+copy)+NSString+*+lineDelimiter;
@property+(nonatomic)+NSUInteger+chunkSize;

-+(id)+initWithFilePath:(NSString+*)aPath;

-+(NSString+*)+readLine;
-+(NSString+*)+readTrimmedLine;

#if+NS_BLOCKS_AVAILABLE
-+(void)+enumerateLinesUsingBlock:(void(%5E)(NSString*,+BOOL+*))block;
#endif

@end|code-block|syntax|javascript|1306032|.m文件：|1306033|#import+"FileChunkReader.h"

@interface+NSData+(DDAdditions)

-+(NSRange)+rangeOfData_dd:(NSData+*)dataToFind;

@end

@implementation+NSData+(DDAdditions)

-+(NSRange)+rangeOfData_dd:(NSData+*)dataToFind+{

++++const+void+*+bytes+=+[self+bytes];
++++NSUInteger+length+=+[self+length];

++++const+void+*+searchBytes+=+[dataToFind+bytes];
++++NSUInteger+searchLength+=+[dataToFind+length];
++++NSUInteger+searchIndex+=+0;

++++NSRange+foundRange+=+{NSNotFound,+searchLength};
++++for+(NSUInteger+index+=+0;+index+<+length;+index%2B%2B)+{
++++++++if+(((char+*)bytes)[index]+==+((char+*)searchBytes)[searchIndex])+{
++++++++++++//the+current+character+matches
++++++++++++if+(foundRange.location+==+NSNotFound)+{
++++++++++++++++foundRange.location+=+index;
++++++++++++}
++++++++++++searchIndex%2B%2B;
++++++++++++if+(searchIndex+>=+searchLength)
++++++++++++{
++++++++++++++++return+foundRange;
++++++++++++}
++++++++}+else+{
++++++++++++searchIndex+=+0;
++++++++++++foundRange.location+=+NSNotFound;
++++++++}
++++}

++++if+(foundRange.location+!=+NSNotFound
++++++++&&+length+<+foundRange.location+%2B+foundRange.length+)
++++{
++++++++//+if+the+dataToFind+is+partially+found+at+the+end+of+[self+bytes],
++++++++//+then+the+loop+above+would+end,+and+indicate+the+dataToFind+is+found
++++++++//+when+it+only+partially+was.
++++++++foundRange.location+=+NSNotFound;
++++}

++++return+foundRange;
}

@end

@implementation+FileChunkReader

@synthesize+lineDelimiter,+chunkSize;

-+(id)+initWithFilePath:(NSString+*)aPath+{
++++if+(self+=+[super+init])+{
++++++++fileHandle+=+[NSFileHandle+fileHandleForReadingAtPath:aPath];
++++++++if+(fileHandle+==+nil)+{
++++++++++++return+nil;
++++++++}

++++++++lineDelimiter+=+@"\n";
++++++++currentOffset+=+0ULL;+//+???
++++++++chunkSize+=+128;
++++++++[fileHandle+seekToEndOfFile];
++++++++totalFileLength+=+[fileHandle+offsetInFile];
++++++++//we+don't+need+to+seek+back,+since+readLine+will+do+that.
++++}
++++return+self;
}

-+(void)+dealloc+{
++++[fileHandle+closeFile];
++++currentOffset+=+0ULL;

}

-+(NSString+*)+readLine+{
++++if+(currentOffset+>=+totalFileLength)
++++{
++++++++return+nil;
++++}

++++@autoreleasepool+{

++++++++NSData+*+newLineData+=+[lineDelimiter+dataUsingEncoding:NSUTF8StringEncoding];
++++++++[fileHandle+seekToFileOffset:currentOffset];
++++++++unsigned+long+long+originalOffset+=+currentOffset;
++++++++NSMutableData+*currentData+=+[[NSMutableData+alloc]+init];
++++++++NSData+*currentLine+=+[[NSData+alloc]+init];
++++++++BOOL+shouldReadMore+=+YES;


++++++++while+(shouldReadMore)+{
++++++++++++if+(currentOffset+>=+totalFileLength)
++++++++++++{
++++++++++++++++break;
++++++++++++}

++++++++++++NSData+*+chunk+=+[fileHandle+readDataOfLength:chunkSize];
++++++++++++[currentData+appendData:chunk];

++++++++++++NSRange+newLineRange+=+[currentData+rangeOfData_dd:newLineData];

++++++++++++if+(newLineRange.location+!=+NSNotFound)+{

++++++++++++++++currentOffset+=+originalOffset+%2B+newLineRange.location+%2B+newLineData.length;
++++++++++++++++currentLine+=+[currentData+subdataWithRange:NSMakeRange(0,+newLineRange.location)];

++++++++++++++++shouldReadMore+=+NO;
++++++++++++}else{
++++++++++++++++currentOffset+%2B=+[chunk+length];
++++++++++++}
++++++++}

++++++++if+(currentLine.length+==+0+&&+currentData.length+>+0)
++++++++{
++++++++++++currentLine+=+currentData;
++++++++}

++++++++return+[[NSString+alloc]+initWithData:currentLine+encoding:NSUTF8StringEncoding];
++++}
}

-+(NSString+*)+readTrimmedLine+{
++++return+[[self+readLine]+stringByTrimmingCharactersInSet:[NSCharacterSet+whitespaceAndNewlineCharacterSet]];
}

#if+NS_BLOCKS_AVAILABLE
-+(void)+enumerateLinesUsingBlock:(void(%5E)(NSString*,+BOOL*))block+{
++++NSString+*+line+=+nil;
++++BOOL+stop+=+NO;
++++while+(stop+==+NO+&&+(line+=+[self+readLine]))+{
++++++++block(line,+&stop);
++++}
}
#endif

@end|1306034|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/users/115730/dave-delong^0|1O|4|1X|2|I|B|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]|$9|13|A|14|B|C]]|D|@$9|15|A|16|1|17]]|E|$]]|$1|F|3|G|5|6|7|18|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|19|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|1A|8|@]|D|@]|E|$M|N]]|$1|O|3|P|5|6|7|1B|8|@]|D|@]|E|$]]|$1|Q|3|R|5|L|7|1C|8|@]|D|@]|E|$M|N]]|$1|S|3|-4|5|6|7|1D|8|@]|D|@]|E|$]]]|T|$U|$5|V|W|X|E|$Y|Z]]]]

I found response by @lukaswelte and code from <a href="https://stackoverflow.com/users/115730/dave-delong">Dave DeLong</a> very helpful. I was looking for a solution to this problem but needed to parse large files by <code>\r\n</code> not just <code>\n</code>. 

The code as written contains a bug if parsing by more than one character. I've changed the code as below.

.h file:

<pre><code>#import &lt;Foundation/Foundation.h&gt;

@interface FileChunkReader : NSObject {
 NSString * filePath;

 NSFileHandle * fileHandle;
 unsigned long long currentOffset;
 unsigned long long totalFileLength;

 NSString * lineDelimiter;
 NSUInteger chunkSize;
}

@property (nonatomic, copy) NSString * lineDelimiter;
@property (nonatomic) NSUInteger chunkSize;

- (id) initWithFilePath:(NSString *)aPath;

- (NSString *) readLine;
- (NSString *) readTrimmedLine;

#if NS_BLOCKS_AVAILABLE
- (void) enumerateLinesUsingBlock:(void(^)(NSString*, BOOL *))block;
#endif

@end
</code></pre>

.m file:

<pre><code>#import "FileChunkReader.h"

@interface NSData (DDAdditions)

- (NSRange) rangeOfData_dd:(NSData *)dataToFind;

@end

@implementation NSData (DDAdditions)

- (NSRange) rangeOfData_dd:(NSData *)dataToFind {

 const void * bytes = [self bytes];
 NSUInteger length = [self length];

 const void * searchBytes = [dataToFind bytes];
 NSUInteger searchLength = [dataToFind length];
 NSUInteger searchIndex = 0;

 NSRange foundRange = {NSNotFound, searchLength};
 for (NSUInteger index = 0; index &lt; length; index++) {
 if (((char *)bytes)[index] == ((char *)searchBytes)[searchIndex]) {
 //the current character matches
 if (foundRange.location == NSNotFound) {
 foundRange.location = index;
 }
 searchIndex++;
 if (searchIndex &gt;= searchLength)
 {
 return foundRange;
 }
 } else {
 searchIndex = 0;
 foundRange.location = NSNotFound;
 }
 }

 if (foundRange.location != NSNotFound
 &amp;&amp; length &lt; foundRange.location + foundRange.length )
 {
 // if the dataToFind is partially found at the end of [self bytes],
 // then the loop above would end, and indicate the dataToFind is found
 // when it only partially was.
 foundRange.location = NSNotFound;
 }

 return foundRange;
}

@end

@implementation FileChunkReader

@synthesize lineDelimiter, chunkSize;

- (id) initWithFilePath:(NSString *)aPath {
 if (self = [super init]) {
 fileHandle = [NSFileHandle fileHandleForReadingAtPath:aPath];
 if (fileHandle == nil) {
 return nil;
 }

 lineDelimiter = @"\n";
 currentOffset = 0ULL; // ???
 chunkSize = 128;
 [fileHandle seekToEndOfFile];
 totalFileLength = [fileHandle offsetInFile];
 //we don't need to seek back, since readLine will do that.
 }
 return self;
}

- (void) dealloc {
 [fileHandle closeFile];
 currentOffset = 0ULL;

}

- (NSString *) readLine {
 if (currentOffset &gt;= totalFileLength)
 {
 return nil;
 }

 @autoreleasepool {

 NSData * newLineData = [lineDelimiter dataUsingEncoding:NSUTF8StringEncoding];
 [fileHandle seekToFileOffset:currentOffset];
 unsigned long long originalOffset = currentOffset;
 NSMutableData *currentData = [[NSMutableData alloc] init];
 NSData *currentLine = [[NSData alloc] init];
 BOOL shouldReadMore = YES;


 while (shouldReadMore) {
 if (currentOffset &gt;= totalFileLength)
 {
 break;
 }

 NSData * chunk = [fileHandle readDataOfLength:chunkSize];
 [currentData appendData:chunk];

 NSRange newLineRange = [currentData rangeOfData_dd:newLineData];

 if (newLineRange.location != NSNotFound) {

 currentOffset = originalOffset + newLineRange.location + newLineData.length;
 currentLine = [currentData subdataWithRange:NSMakeRange(0, newLineRange.location)];

 shouldReadMore = NO;
 }else{
 currentOffset += [chunk length];
 }
 }

 if (currentLine.length == 0 &amp;&amp; currentData.length &gt; 0)
 {
 currentLine = currentData;
 }

 return [[NSString alloc] initWithData:currentLine encoding:NSUTF8StringEncoding];
 }
}

- (NSString *) readTrimmedLine {
 return [[self readLine] stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
}

#if NS_BLOCKS_AVAILABLE
- (void) enumerateLinesUsingBlock:(void(^)(NSString*, BOOL*))block {
 NSString * line = nil;
 BOOL stop = NO;
 while (stop == NO &amp;&amp; (line = [self readLine])) {
 block(line, &amp;stop);
 }
}
#endif

@end
</code></pre>

blocks|key|1521170|text|我添加这个是因为我尝试过的所有其他答案都以这样或那样的方式失败了。下面的方法可以处理大文件、任意长行和空行。它已经用实际内容进行了测试，并将从输出中去掉换行符。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1521171|-+(NSString*)readLineFromFile:(FILE+*)file
{
++++char+buffer[4096];
++++NSMutableString+*result+=+[NSMutableString+stringWithCapacity:1000];

++++int+charsRead;
++++do+{
++++++++if(fscanf(file,+"%254095[%5E\r\n]%25n%25*[\n\r]",+buffer,+&charsRead)+==+1)+{
++++++++++++[result+appendFormat:@"%25s",+buffer];
++++++++}
++++++++else+{
++++++++++++break;
++++++++}
++++}+while(charsRead+==+4095);

++++return+result.length+?+result+:+nil;
}|code-block|syntax|javascript|1521172|功劳归功于@Adam+Rosenfield和@sooop|1521173|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

I am adding this because all other answers I tried fell short one way or another. The following method can handle large files, arbitrary long lines, as well as empty lines. It has been tested with actual content and will strip out newline character from the output.

<pre><code>- (NSString*)readLineFromFile:(FILE *)file
{
 char buffer[4096];
 NSMutableString *result = [NSMutableString stringWithCapacity:1000];

 int charsRead;
 do {
 if(fscanf(file, "%4095[^\r\n]%n%*[\n\r]", buffer, &amp;charsRead) == 1) {
 [result appendFormat:@"%s", buffer];
 }
 else {
 break;
 }
 } while(charsRead == 4095);

 return result.length ? result : nil;
}
</code></pre>

Credit goes to @Adam Rosenfield and @sooop

blocks|key|1521225|text|我看到许多这样的答案都依赖于将整个文本文件读入内存，而不是一次读取一个块。这是我在现代Swift中的解决方案，使用FileHandle保持较低的内存影响：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1521226|enum+MyError+{
++++case+invalidTextFormat
}

extension+FileHandle+{

++++func+readLine(maxLength:+Int)+throws+->+String+{

++++++++//+Read+in+a+string+of+up+to+the+maximum+length
++++++++let+offset+=+offsetInFile
++++++++let+data+=+readData(ofLength:+maxLength)
++++++++guard+let+string+=+String(data:+data,+encoding:+.utf8)+else+{
++++++++++++throw+MyError.invalidTextFormat
++++++++}

++++++++//+Check+for+carriage+returns;+if+none,+this+is+the+whole+string
++++++++let+substring:+String
++++++++if+let+subindex+=+string.firstIndex(of:+"\n")+{
++++++++++++substring+=+String(string[string.startIndex+...+subindex])
++++++++}+else+{
++++++++++++substring+=+string
++++++++}

++++++++//+Wind+back+to+the+correct+offset+so+that+we+don't+miss+any+lines
++++++++guard+let+dataCount+=+substring.data(using:+.utf8,+allowLossyConversion:+false)?.count+else+{
++++++++++++throw+MyError.invalidTextFormat
++++++++}
++++++++try+seek(toOffset:+offset+%2B+UInt64(dataCount))
++++++++return+substring
++++}

}|code-block|syntax|javascript|1521227|请注意，这保留了行尾的回车，因此根据您的需要，您可能希望调整代码以删除它。|1521228|用法:只需打开一个指向目标文本文件的文件句柄，并以适当的最大长度调用readLine+-+1024是纯文本的标准长度，但我将其保留为开放的，以防您知道它会更短。请注意，该命令不会溢出文件的末尾，因此，如果您打算解析整个文件，则可能需要手动检查是否尚未到达该文件。下面是一些示例代码，展示了如何在myFileURL中打开一个文件，并逐行读取该文件直到文件结束。|offset|length|style|CODE|1521229|do+{
++++let+handle+=+try+FileHandle(forReadingFrom:+myFileURL)
++++try+handle.seekToEndOfFile()
++++let+eof+=+handle.offsetInFile
++++try+handle.seek(toFileOffset:+0)

++++while+handle.offsetInFile+<+eof+{
++++++++let+line+=+try+handle.readLine(maxLength:+1024)
++++++++//+Do+something+with+the+string+here
++++}
++++try+handle.close()
catch+let+error+{
++++print("Error+reading+file:+\(error.localizedDescription)"
}|1521230|entityMap^0|0|0|0|Y|8|43|9|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|V|8|@$K|W|L|X|M|N]|$K|Y|L|Z|M|N]]|9|@]|A|$]]|$1|O|3|P|5|D|7|10|8|@]|9|@]|A|$E|F]]|$1|Q|3|-4|5|6|7|11|8|@]|9|@]|A|$]]]|R|$]]

I see a lot of these answers rely on reading the whole text file into memory instead of taking it one chunk at a time. Here's my solution in nice modern Swift, using FileHandle to keep memory impact low:

<pre><code>enum MyError {
 case invalidTextFormat
}

extension FileHandle {

 func readLine(maxLength: Int) throws -&gt; String {

 // Read in a string of up to the maximum length
 let offset = offsetInFile
 let data = readData(ofLength: maxLength)
 guard let string = String(data: data, encoding: .utf8) else {
 throw MyError.invalidTextFormat
 }

 // Check for carriage returns; if none, this is the whole string
 let substring: String
 if let subindex = string.firstIndex(of: "\n") {
 substring = String(string[string.startIndex ... subindex])
 } else {
 substring = string
 }

 // Wind back to the correct offset so that we don't miss any lines
 guard let dataCount = substring.data(using: .utf8, allowLossyConversion: false)?.count else {
 throw MyError.invalidTextFormat
 }
 try seek(toOffset: offset + UInt64(dataCount))
 return substring
 }

}
</code></pre>

Note that this preserves the carriage return at the end of the line, so depending on your needs you may want to adjust the code to remove it.

Usage: simply open a file handle to your target text file and call <code>readLine</code> with a suitable maximum length - 1024 is standard for plain text, but I left it open in case you know it will be shorter. Note that the command will not overflow the end of the file, so you may have to check manually that you've not reached it if you intend to parse the entire thing. Here's some sample code that shows how to open a file at <code>myFileURL</code> and read it line-by-line until the end.

<pre><code>do {
 let handle = try FileHandle(forReadingFrom: myFileURL)
 try handle.seekToEndOfFile()
 let eof = handle.offsetInFile
 try handle.seek(toFileOffset: 0)

 while handle.offsetInFile &lt; eof {
 let line = try handle.readLine(maxLength: 1024)
 // Do something with the string here
 }
 try handle.close()
catch let error {
 print("Error reading file: \(error.localizedDescription)"
}
</code></pre>

blocks|key|1520838|text|下面是我用来处理较小文件的一个很好的简单解决方案：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1520839|NSString+*path+=+[[NSBundle+mainBundle]+pathForResource:@"Terrain1"+ofType:@"txt"];
NSString+*contents+=+[NSString+stringWithContentsOfFile:path+encoding:NSASCIIStringEncoding+error:nil];
NSArray+*lines+=+[contents+componentsSeparatedByCharactersInSet:[NSCharacterSet+characterSetWithCharactersInString:@"\r\n"]];
for+(NSString*+line+in+lines)+{
++++if+(line.length)+{
++++++++NSLog(@"line:+%25@",+line);
++++}
}|code-block|syntax|javascript|1520840|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Here's a nice simple solution i use for smaller files:

<pre><code>NSString *path = [[NSBundle mainBundle] pathForResource:@"Terrain1" ofType:@"txt"];
NSString *contents = [NSString stringWithContentsOfFile:path encoding:NSASCIIStringEncoding error:nil];
NSArray *lines = [contents componentsSeparatedByCharactersInSet:[NSCharacterSet characterSetWithCharactersInString:@"\r\n"]];
for (NSString* line in lines) {
 if (line.length) {
 NSLog(@"line: %@", line);
 }
}
</code></pre>

blocks|key|1305745|text|使用这个脚本，它工作得很好：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1305746|NSString+*path+=+@"/Users/xxx/Desktop/names.txt";
NSError+*error;
NSString+*stringFromFileAtPath+=+[NSString+stringWithContentsOfFile:+path
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++encoding:+NSUTF8StringEncoding
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++error:+&error];
if+(stringFromFileAtPath+==+nil)+{
++++NSLog(@"Error+reading+file+at+%25@\n%25@",+path,+[error+localizedFailureReason]);
}
NSLog(@"Contents:%25@",+stringFromFileAtPath);|code-block|syntax|javascript|1305747|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Use this script, it works great: 

<pre><code>NSString *path = @"/Users/xxx/Desktop/names.txt";
NSError *error;
NSString *stringFromFileAtPath = [NSString stringWithContentsOfFile: path
 encoding: NSUTF8StringEncoding
 error: &amp;error];
if (stringFromFileAtPath == nil) {
 NSLog(@"Error reading file at %@\n%@", path, [error localizedFailureReason]);
}
NSLog(@"Contents:%@", stringFromFileAtPath);
</code></pre>

What is the appropriate way of dealing with large text files in Objective-C? Let's say I need to read each line separately and want to treat each line as an NSString. What is the most efficient way of doing this?

One solution is using the NSString method:

<pre><code>+ (id)stringWithContentsOfFile:(NSString *)path 
 encoding:(NSStringEncoding)enc 
 error:(NSError **)error 
</code></pre>

and then split the lines with a newline separator, and then iterate over the elements in the array. However, this seems fairly inefficient. Is there no easy way to treat the file as a stream, enumerating over each line, instead of just reading it all in at once? Kinda like Java's java.io.BufferedReader.

Objective-C: Reading a file line by line

内存映射

Objective-C

Swift

Java

Unix

在Objective-C中处理大型文本文件的适当方式是什么？假设我需要单独读取每一行，并希望将每一行都视为一个NSString。执行此操作的最有效方法是什么？一种解决方案是使用NSString方法：+ (id)stringWithContentsOfFile:(NSString *)path       encoding:(NSStringEncoding)enc       error:(NSE

问Objective-C:逐行读取文件
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回答 13

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