without - program to find size of file in c++

How can I get a file's size in C? (6)

Possible Duplicate:
How do you determine the size of a file in C?

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 alloc using malloc(). Just writing malloc(10000*sizeof(char)); is IMHO a bad idea.

Using standard library:

Assuming that your implementation meaningfully supports SEEK_END:

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


You can use stat (if you know the filename), or fstat (if you have the file descriptor).

Here is an example for stat:

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


You can use GetFileSize or GetFileSizeEx.

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

#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 += 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));
      b = b2;
  *buf = b;
  return n;

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

I ended up just making a short and sweet fsize function(note, no error checking)

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;

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 /dev/null)

If you have the file descriptor fstat() returns a stat structure which contain the file size.

#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;

You need to seek to the end of the file and then ask for the position:

fseek(fp, 0L, SEEK_END);
sz = ftell(fp);

You can then seek back, e.g.:

fseek(fp, 0L, SEEK_SET);

or (if seeking to go to the beginning)


#include <stdio.h>

#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);

    return 0;