blocks|key|1491391|text|您需要查找到文件的末尾，然后询问位置：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1491392|fseek(fp,+0L,+SEEK_END);
sz+=+ftell(fp);|code-block|syntax|javascript|1491393|然后，您可以向后查找，例如：|1491394|fseek(fp,+0L,+SEEK_SET);|1491395|或者(如果要从头开始)|1491396|rewind(fp);|1491397|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

<p>You need to seek to the end of the file and then ask for the position:</p>

<pre><code>fseek(fp, 0L, SEEK_END);
sz = ftell(fp);
</code></pre>

<p>You can then seek back, e.g.:</p>

<pre><code>fseek(fp, 0L, SEEK_SET);
</code></pre>

<p>or (if seeking to go to the beginning)</p>

<pre><code>rewind(fp);
</code></pre>


blocks|key|1706500|text|使用标准库：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1706501|假设您的实现很有意义地支持SEEK_END：|1706502|fseek(f,+0,+SEEK_END);+//+seek+to+end+of+file
size+=+ftell(f);+//+get+current+file+pointer
fseek(f,+0,+SEEK_SET);+//+seek+back+to+beginning+of+file
//+proceed+with+allocating+memory+and+reading+the+file|code-block|syntax|javascript|1706503|Linux/POSIX：|1706504|您可以使用stat+(如果您知道文件名)或fstat+(如果您有文件描述符)。|offset|length|style|CODE|1706505|以下是stat的示例：|1706506|#include+<sys/stat.h>
struct+stat+st;
stat(filename,+&st);
size+=+st.st_size;|1706507|Win32：|1706508|您可以使用GetFileSize或GetFileSizeEx。|1706509|entityMap|0|LINK|mutability|MUTABLE|url|https://msdn.microsoft.com/en-us/library/windows/desktop/aa364955(v=vs.85).aspx|1|https://msdn.microsoft.com/en-us/library/windows/desktop/aa364957(v=vs.85).aspx)^0|0|0|0|0|5|4|L|5|0|0|0|0|5|B|0|H|D|1|0^^$0|@$1|2|3|4|5|6|7|18|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|19|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|1A|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|1B|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|1C|8|@$M|1D|N|1E|O|P]|$M|1F|N|1G|O|P]]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1H|8|@]|9|@]|A|$]]|$1|S|3|T|5|F|7|1I|8|@]|9|@]|A|$G|H]]|$1|U|3|V|5|6|7|1J|8|@]|9|@]|A|$]]|$1|W|3|X|5|6|7|1K|8|@]|9|@$M|1L|N|1M|1|1N]|$M|1O|N|1P|1|1Q]]|A|$]]|$1|Y|3|-4|5|6|7|1R|8|@]|9|@]|A|$]]]|Z|$10|$5|11|12|13|A|$14|15]]|16|$5|11|12|13|A|$14|17]]]]

<h2>Using standard library:</h2>

<p>Assuming that your implementation meaningfully supports SEEK_END:</p>

<pre><code>fseek(f, 0, SEEK_END); // seek to end of file
size = ftell(f); // get current file pointer
fseek(f, 0, SEEK_SET); // seek back to beginning of file
// proceed with allocating memory and reading the file
</code></pre>

<h2>Linux/POSIX:</h2>

<p>You can use <code>stat</code> (if you know the filename), or <code>fstat</code> (if you have the file descriptor).</p>

<p>Here is an example for stat:</p>

<pre><code>#include &lt;sys/stat.h&gt;
struct stat st;
stat(filename, &amp;st);
size = st.st_size;
</code></pre>

<h2>Win32:</h2>

<p>You can use <a href="https://msdn.microsoft.com/en-us/library/windows/desktop/aa364955(v=vs.85).aspx" rel="noreferrer">GetFileSize</a> or <a href="https://msdn.microsoft.com/en-us/library/windows/desktop/aa364957(v=vs.85).aspx" rel="noreferrer">GetFileSizeEx</a>.</p>


blocks|key|1491463|text|如果有文件描述符，fstat()将返回一个包含文件大小的stat结构。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1491464|#include+<sys/types.h>
#include+<sys/stat.h>
#include+<unistd.h>

//+fd+=+fileno(f);+//if+you+have+a+stream+(e.g.+from+fopen),+not+a+file+descriptor.
struct+stat+buf;
fstat(fd,+&buf);
off_t+size+=+buf.st_size;|code-block|syntax|javascript|1491465|entityMap^0|9|7|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

<p>If you have the file descriptor <code>fstat()</code> returns a stat structure which contain the file size.</p>

<pre><code>#include &lt;sys/types.h&gt;
#include &lt;sys/stat.h&gt;
#include &lt;unistd.h&gt;

// fd = fileno(f); //if you have a stream (e.g. from fopen), not a file descriptor.
struct stat buf;
fstat(fd, &amp;buf);
off_t size = buf.st_size;
</code></pre>


blocks|key|1491477|text|#include+<stdio.h>

#define+MAXNUMBER+1024

int+main()
{
++++int+i;
++++char+a[MAXNUMBER];

++++FILE+*fp+=+popen("du+-b++/bin/bash",+"r");

++++while((a[i%2B%2B]+=+getc(fp))!=+9)
++++++++;

++++a[i]+='\0';

++++printf("+a+is+%25s\n",+a);

++++pclose(fp);
++++return+0;
}++|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1491478|HTH|unstyled|1491479|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|J|8|@]|9|@]|A|$]]|$1|G|3|-4|5|F|7|K|8|@]|9|@]|A|$]]]|H|$]]

<pre><code>#include &lt;stdio.h&gt;

#define MAXNUMBER 1024

int main()
{
    int i;
    char a[MAXNUMBER];

    FILE *fp = popen("du -b  /bin/bash", "r");

    while((a[i++] = getc(fp))!= 9)
        ;

    a[i] ='\0';

    printf(" a is %s\n", a);

    pclose(fp);
    return 0;
}  
</code></pre>

<p>HTH</p>


blocks|key|1706587|text|您是否考虑过不计算文件大小，并在必要时仅增加阵列大小？下面是一个例子(省略了错误检查)：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1706588|#define+CHUNK+1024

/*+Read+the+contents+of+a+file+into+a+buffer.++Return+the+size+of+the+file+
+*+and+set+buf+to+point+to+a+buffer+allocated+with+malloc+that+contains++
+*+the+file+contents.
+*/
int+read_file(FILE+*fp,+char+**buf)+
{
++int+n,+np;
++char+*b,+*b2;

++n+=+CHUNK;
++np+=+n;
++b+=+malloc(sizeof(char)*n);
++while+((r+=+fread(b,+sizeof(char),+CHUNK,+fp))+>+0)+{
++++n+%2B=+r;
++++if+(np+-+n+<+CHUNK)+{+
++++++np+*=+2;++++++++++++++++++++++//+buffer+is+too+small,+the+next+read+could+overflow!
++++++b2+=+malloc(np*sizeof(char));
++++++memcpy(b2,+b,+n+*+sizeof(char));
++++++free(b);
++++++b+=+b2;
++++}
++}
++*buf+=+b;
++return+n;
}|code-block|syntax|javascript|1706589|这样做的好处是，即使对于无法获得文件大小(如stdin)的流，也能正常工作。|1706590|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|$]]

<p>Have you considered not computing the file size and just growing the array if necessary?  Here's an example (with error checking ommitted):</p>

<pre><code>#define CHUNK 1024

/* Read the contents of a file into a buffer.  Return the size of the file 
 * and set buf to point to a buffer allocated with malloc that contains  
 * the file contents.
 */
int read_file(FILE *fp, char **buf) 
{
  int n, np;
  char *b, *b2;

  n = CHUNK;
  np = n;
  b = malloc(sizeof(char)*n);
  while ((r = fread(b, sizeof(char), CHUNK, fp)) &gt; 0) {
    n += r;
    if (np - n &lt; CHUNK) { 
      np *= 2;                      // buffer is too small, the next read could overflow!
      b2 = malloc(np*sizeof(char));
      memcpy(b2, b, n * sizeof(char));
      free(b);
      b = b2;
    }
  }
  *buf = b;
  return n;
}
</code></pre>

<p>This has the advantage of working even for streams in which it is impossible to get the file size (like stdin).</p>


blocks|key|1491565|text|我最终只做了一个简短的fsize函数(注意，没有错误检查)|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1491566|int+fsize(FILE+*fp){
++++int+prev=ftell(fp);
++++fseek(fp,+0L,+SEEK_END);
++++int+sz=ftell(fp);
++++fseek(fp,prev,SEEK_SET);+//go+back+to+where+we+were
++++return+sz;
}|code-block|syntax|javascript|1491567|标准C库没有这样的函数有点傻，但我能理解为什么它很难，因为不是每个“文件”都有一个大小(例如/dev/null)|1491568|entityMap^0|B|5|0|0|1A|9|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|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|M|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|N|$]]

<p>I ended up just making a short and sweet <code>fsize</code> function(note, no error checking)</p>

<pre><code>int fsize(FILE *fp){
    int prev=ftell(fp);
    fseek(fp, 0L, SEEK_END);
    int sz=ftell(fp);
    fseek(fp,prev,SEEK_SET); //go back to where we were
    return sz;
}
</code></pre>

<p>It's kind of silly that the standard C library doesn't have such a function, but I can see why it'd be difficult as not every "file" has a size(for instance <code>/dev/null</code>) </p>


<p>How can I find out the size of a file I opened with an application written in C ? 
I would like to know the size, because I want to put the content of the loaded file into a string, which I allocate using <code>malloc()</code>. Just writing <code>malloc(10000*sizeof(char));</code> is IMHO a bad idea. </p>


How can I get a file's size in C?

Linux

我怎样才能知道我用C写的应用程序打开的文件的大小？我想知道文件的大小，因为我想将加载文件的内容放入一个字符串中，这个字符串是使用malloc()分配的。仅仅写malloc(10000*sizeof(char));不是一个好主意。

问如何在C中获取文件的大小？
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