size of file in c

1If you have the file stream (FILE * f):
2
3fseek(f, 0, SEEK_END); // seek to end of file
4size = ftell(f); // get current file pointer
5fseek(f, 0, SEEK_SET); // seek back to beginning of file
6// proceed with allocating memory and reading the file
7
8Or,
9
10#include <sys/types.h>
11#include <sys/stat.h>
12#include <unistd.h>
13fd = fileno(f); 
14struct stat buf;
15fstat(fd, &buf);
16int size = buf.st_size;
17
18Or, use stat, if you know the filename:
19
20#include <sys/stat.h>
21struct stat st;
22stat(filename, &st);
23size = st.st_size;

1If you use :
2
3/** 
4	Pay attention to return type! 
5	ftell returns long, which can only be used for files under 2GB. 
6**/
7fseek(f, 0, SEEK_END); // seek to end of file
8size = ftell(f); // get current file pointer
9fseek(f, 0, SEEK_SET); // seek back to beginning of file
10
11// If u want to get file of large size, use stat() instead
12struct stat buf;
13if(stat(filename, &buf) == -1){
14   return -1;
15}
16return (ssize_t)buf.st_size;

1// C program to find the size of file 
2#include <stdio.h> 
3
4long int findSize(char file_name[]) 
5{ 
6	// opening the file in read mode 
7	FILE* fp = fopen(file_name, "r"); 
8
9	// checking if the file exist or not 
10	if (fp == NULL) { 
11		printf("File Not Found!\n"); 
12		return -1; 
13	} 
14
15	fseek(fp, 0L, SEEK_END); 
16
17	// calculating the size of the file 
18	long int res = ftell(fp); 
19
20	// closing the file 
21	fclose(fp); 
22
23	return res; 
24} 
25
26// Driver code 
27int main() 
28{ 
29	char file_name[] = { "a.txt" }; 
30	long int res = findSize(file_name); 
31	if (res != -1) 
32		printf("Size of the file is %ld bytes \n", res); 
33	return 0; 
34} 
35