andrewrk andrewrk - 2 months ago 5
C Question

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

How can I figure out the size of a file, in bytes?

#include <stdio.h>

unsigned int fsize(char* file){
//what goes here?
}

Answer

Based on NilObject's code:

#include <sys/stat.h>

off_t fsize(const char *filename) {
    struct stat st; 

    if (stat(filename, &st) == 0)
        return st.st_size;

    return -1; 
}

Changes:

  • Made the filename argument a const char.
  • Corrected the struct stat definition, which was missing the variable name.
  • Returns -1 on error instead of 0, which would be ambiguous for an empty file. off_t is a signed type so this is possible.

If you want fsize() to print a message on error, you can use this:

#include <sys/stat.h>
#include <string.h>
#include <stdio.h>
#include <errno.h>

off_t fsize(const char *filename) {
    struct stat st;

    if (stat(filename, &st) == 0)
        return st.st_size;

    fprintf(stderr, "Cannot determine size of %s: %s\n",
            filename, strerror(errno));

    return -1;
}

On 32-bit systems you should compile this with the option -D_FILE_OFFSET_BITS=64, otherwise off_t will only hold values up to 2 GB. See the "Using LFS" section of Large File Support in Linux for details.

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