blocks|key|788932|text|268566528是您期望的值，还是您期望的528值？如果正确的值是528，那么字节顺序是大端的，但是cpu是小端的，字节需要颠倒。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|788933|因此，如果正确的值应该是528，那么：|788934|NSData+*data4+=+[completeData+subdataWithRange:NSMakeRange(0,+4)];
int+value+=+CFSwapInt32BigToHost(*(int*)([data4+bytes]));|code-block|syntax|javascript|788935|另请注意，网络标准顺序为big-endian。|788936|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|O|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Is 268566528 the value you expect or perhaps you expect 528? If the correct value is 528 then the byte order is big-endian but the cpu is little-endian, the bytes need to be reversed.

So, if the correct value should be 528 then:

<pre><code>NSData *data4 = [completeData subdataWithRange:NSMakeRange(0, 4)];
int value = CFSwapInt32BigToHost(*(int*)([data4 bytes]));
</code></pre>

Also note that network standard order is big-endian.

blocks|key|572703|text|该语句将提供前16个字节的数据，而不是4个字节。要获得前4个字节，您需要将语句修改为：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|572704|fourByteData+=+[completeData+subdataWithRange:NSMakeRange(0,+4)];|code-block|syntax|javascript|572705|要将数据从NSData对象读取到整数，您可以执行以下操作：|572706|int+theInteger;
[completeData+getBytes:&theInteger+length:sizeof(theInteger)];|572707|如果您只是将其转换为整数，则不需要获取前4个字节。您可以通过上面的两行代码和您的completeData接收器直接执行此操作|offset|length|style|CODE|572708|entityMap^0|0|0|0|0|14|C|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]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@$M|X|N|Y|O|P]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

That statement would give you the first 16 bytes of data, not 4. To get the first 4 bytes you need to modify your statement to:

<pre><code>fourByteData = [completeData subdataWithRange:NSMakeRange(0, 4)];
</code></pre>

To read the data from the NSData Object to an integer you could do something like:

<pre><code>int theInteger;
[completeData getBytes:&amp;theInteger length:sizeof(theInteger)];
</code></pre>

You do not need to get the first 4 bytes if you are just converting it to an integer. You can do this directly from the two lines above and your <code>completeData</code> receiver

blocks|key|788874|text|不，您将获得16字节的数据，因为范围是从偏移量0开始，然后是16字节。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|788875|如果你有一个4字节的NSData实例，那么你可以像这样做一个简单的类型转换：|offset|length|style|CODE|788876|int+value+=+*(int*)([data+bytes]);|code-block|syntax|javascript|788877|entityMap^0|0|A|6|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@$D|Q|E|R|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|S|8|@]|9|@]|A|$K|L]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

No you will get 16 bytes of data, since the range is from offset 0 and then 16 bytes.

If you had a <code>NSData</code> instance with 4 bytes then you could do a simple type cast like this:

<pre><code>int value = *(int*)([data bytes]);
</code></pre>

blocks|key|788946|text|-+(unsigned)parseIntFromData:(NSData+*)data{

++++NSString+*dataDescription+=+[data+description];
++++NSString+*dataAsString+=+[dataDescription+substringWithRange:NSMakeRange(1,+[dataDescription+length]-2)];

++++unsigned+intData+=+0;
++++NSScanner+*scanner+=+[NSScanner+scannerWithString:dataAsString];
++++[scanner+scanHexInt:&intData];

++++return+intData;
}

int+numberOfChunks+=+[self+parseIntFromData:data];|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|788947|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>- (unsigned)parseIntFromData:(NSData *)data{

 NSString *dataDescription = [data description];
 NSString *dataAsString = [dataDescription substringWithRange:NSMakeRange(1, [dataDescription length]-2)];

 unsigned intData = 0;
 NSScanner *scanner = [NSScanner scannerWithString:dataAsString];
 [scanner scanHexInt:&amp;intData];

 return intData;
}

int numberOfChunks = [self parseIntFromData:data];
</code></pre>

blocks|key|572883|text|iOS整数将最低有效字节存储在第一个字节中，将最低有效字节存储在最后一个字节中。我有转换例程来测试所有这些东西。在这里查看，|type|unstyled|depth|inlineStyleRanges|entityRanges|data|572884|测试...|572885|int+i+=+2342342;
++++NSData+*+d1+=+[Util+dataFromInt:i];+//+{[MSB],+...,+...+,[LSB]}+<0023bdc6>
++++NSData+*+d2+=+[NSData+dataWithBytes:&i+length:4];++//+{[LSB],+...,+...+,[MSB]}+<c6bd2300>
++++int+ci1+=+[Util+intFromData:d1];
++++int+ci2+=+[Util+intFromDataReverse:d2];|code-block|syntax|javascript|572886|Util.m|572887|%2B+(NSData+*)+dataFromInt:(int)num+{
++++unsigned+char+*+arr+=+(unsigned+char+*)+malloc(sizeof(num)+*+sizeof(unsigned+char));
++++for+(int+i+=+sizeof(num)+-+1+;+i+>=+0;+i+--)+{
++++++++arr[i]+=+num+&+0xFF;
++++++++num+=+num+>>+8;
++++}
++++NSData+*+data+=+[NSData+dataWithBytes:arr+length:sizeof(num)];
++++free(arr);
++++return+data;
}

//+{[MSB],+...,+...+,[LSB]}
%2B+(int)+intFromData:(NSData+*)data
{
++++int+intSize+=+sizeof(int);+//+change+it+to+fixe+length
++++unsigned+char+*+buffer+=+malloc(intSize+*+sizeof(unsigned+char));
++++[data+getBytes:buffer+length:intSize];
++++int+num+=+0;
++++for+(int+i+=+0;+i+<+intSize;+i%2B%2B)+{
++++++++num+=+(num+<<+8)+%2B+buffer[i];
++++}
++++free(buffer);
++++return+num;
}

//+{[LSB],+...,+...+,[MSB]}
%2B+(int)+intFromDataReverse:(NSData+*)data
{
++++int+intSize+=+sizeof(int);//+change+it+to+fixe+length
++++unsigned+char+*+buffer+=+malloc(intSize+*+sizeof(unsigned+char));
++++[data+getBytes:buffer+length:intSize];
++++int+num+=+0;
++++for+(int+i+=+intSize+-+1;+i+>=+0;+i--)+{
++++++++num+=+(num+<<+8)+%2B+buffer[i];
++++}
++++free(buffer);
++++return+num;
}|572888|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|$]]

iOS integer stores LSB (lowest significant byte) in the first byte and MSB in the last byte. I have conversion routine to test all those things. check here,

Test ... 

<pre><code>int i = 2342342;
 NSData * d1 = [Util dataFromInt:i]; // {[MSB], ..., ... ,[LSB]} &lt;0023bdc6&gt;
 NSData * d2 = [NSData dataWithBytes:&amp;i length:4]; // {[LSB], ..., ... ,[MSB]} &lt;c6bd2300&gt;
 int ci1 = [Util intFromData:d1];
 int ci2 = [Util intFromDataReverse:d2];
</code></pre>

Util.m

<pre><code>+ (NSData *) dataFromInt:(int)num {
 unsigned char * arr = (unsigned char *) malloc(sizeof(num) * sizeof(unsigned char));
 for (int i = sizeof(num) - 1 ; i &gt;= 0; i --) {
 arr[i] = num &amp; 0xFF;
 num = num &gt;&gt; 8;
 }
 NSData * data = [NSData dataWithBytes:arr length:sizeof(num)];
 free(arr);
 return data;
}

// {[MSB], ..., ... ,[LSB]}
+ (int) intFromData:(NSData *)data
{
 int intSize = sizeof(int); // change it to fixe length
 unsigned char * buffer = malloc(intSize * sizeof(unsigned char));
 [data getBytes:buffer length:intSize];
 int num = 0;
 for (int i = 0; i &lt; intSize; i++) {
 num = (num &lt;&lt; 8) + buffer[i];
 }
 free(buffer);
 return num;
}

// {[LSB], ..., ... ,[MSB]}
+ (int) intFromDataReverse:(NSData *)data
{
 int intSize = sizeof(int);// change it to fixe length
 unsigned char * buffer = malloc(intSize * sizeof(unsigned char));
 [data getBytes:buffer length:intSize];
 int num = 0;
 for (int i = intSize - 1; i &gt;= 0; i--) {
 num = (num &lt;&lt; 8) + buffer[i];
 }
 free(buffer);
 return num;
}
</code></pre>

blocks|key|572967|text|它取决于您要转换的数据的字节顺序表示法，它与设备的字节顺序表示法相关。wiki+on+Endianness|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|572968|为了简单起见，你需要检查两个方法|572969|NSData+*data4+=+[completeData+subdataWithRange:NSMakeRange(0,+4)];
int+value+=+CFSwapInt32BigToHost(*(int*)([data4+bytes]));|code-block|syntax|javascript|572970|或|572971|NSData+*data4+=+[completeData+subdataWithRange:NSMakeRange(0,+4)];
int+value+=+CFSwapInt32LittleToHost(*(int*)([data4+bytes]));|572972|并在解析数据时检查哪一个更有意义。|572973|entityMap|0|LINK|mutability|MUTABLE|url|https://en.wikipedia.org/wiki/Endianness^0|Z|I|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@$A|Z|B|10|1|11]]|C|$]]|$1|D|3|E|5|6|7|12|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|13|8|@]|9|@]|C|$I|J]]|$1|K|3|L|5|6|7|14|8|@]|9|@]|C|$]]|$1|M|3|N|5|H|7|15|8|@]|9|@]|C|$I|J]]|$1|O|3|P|5|6|7|16|8|@]|9|@]|C|$]]|$1|Q|3|-4|5|6|7|17|8|@]|9|@]|C|$]]]|R|$S|$5|T|U|V|C|$W|X]]]]

It depends on the Endianness notation of the data you want to convert, in relation to your device Endianness notation.
<a href="https://en.wikipedia.org/wiki/Endianness" rel="nofollow">wiki on Endianness</a>

To keep it simple you need to check does two method

<pre><code>NSData *data4 = [completeData subdataWithRange:NSMakeRange(0, 4)];
int value = CFSwapInt32BigToHost(*(int*)([data4 bytes]));
</code></pre>

or

<pre><code>NSData *data4 = [completeData subdataWithRange:NSMakeRange(0, 4)];
int value = CFSwapInt32LittleToHost(*(int*)([data4 bytes]));
</code></pre>

And check which one make more sense when you parse the data.

I've an NSData object, the length is 4 bytes .These four bytes i'm extracting from another NSData object using ,

<pre><code>fourByteData=[completeData subdataWithRange:NSMakeRange(0, 16)];
</code></pre>

My first question is, will the above statement provide me the first four bytes of complete data.

If Yes, then how to convert all these bytes to an equivalent int.

Converting NSData to int

我有一个NSData对象，它的长度是4字节，我是从另一个NSData对象中提取的，fourByteData=[completeData subdataWithRange:NSMakeRange(0, 16)];我的第一个问题是，上面的语句会提供完整数据的前四个字节吗？如果为Yes，则如何将所有这些字节转换为等效的int。

问将NSData转换为int
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