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

Question

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

#include <stdio.h>

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

Answer 1

If you're fine with using the std c library:

#include <sys/stat.h>
off_t fsize(char *file) {
    struct stat filestat;
    if (stat(file, &filestat) == 0) {
        return filestat.st_size;
    }
    return 0;
}

Answer 2

You can open the file, go to 0 offset relative from the bottom of the file with

#define SEEKBOTTOM   2

fseek(handle, 0, SEEKBOTTOM)  

the value returned from fseek is the size of the file.

I didn't code in C for a long time, but I think it should work.

Answer 3

And if you're building a Windows app, use the GetFileSizeEx API as CRT file I/O is messy, especially for determining file length, due to peculiarities in file representations on different systems ;)

Answer 4

Try this --

fseek(fp, 0, SEEK_END);
unsigned long int file_size = ftell(fp);
rewind(fp);

What this does is first, seek to the end of the file; then, report where the file pointer is. Lastly (this is optional) it rewinds back to the beginning of the file. Note that fp should be a binary stream.

file_size contains the number of bytes the file contains. Note that since (according to climits.h) the unsigned long type is limited to 4294967295 bytes (4 gigabytes) you'll need to find a different variable type if you're likely to deal with files larger than that.

Answer 5

Looking at the question, ftell can easily get the number of bytes.

  long size ;
  size = ftell(FILENAME);
  printf("total size is %ld bytes",size);

Answer 6

Based on NilObject's code:

#include <sys/stat.h>
#include <sys/types.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 <sys/types.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.