how to know swap file size in linux code example

Example 1: find the size of file in linux

ls -l filename   #Displays Size of the specified file
ls -l *          #Displays Size of All the files in the current directory
ls -al *         #Displays Size of All the files including hidden files in the current directory
ls -al dir/      #Displays Size of All the files including hidden files in the 'dir' directory

Example 2: how to check the size of a file in linux c

If you have the file stream (FILE * f):

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

Or,

#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
fd = fileno(f); 
struct stat buf;
fstat(fd, &buf);
int size = buf.st_size;

Or, use stat, if you know the filename:

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