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

On Unix-like systems, you can use POSIX system calls: stat on a path, or fstat on an already-open file descriptor (POSIX man page, Linux man page).
(Get a file descriptor from open(2), or fileno(FILE*) on a stdio stream).

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.