Measure a small seekable binary file.

C: Seek to the end and inspect ftell, checking both operations for errors.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <stdint.h>
#include <stdbool.h>
#include <errno.h>
#include <limits.h>
#include <math.h>
#include <time.h>

int main(void) {
    FILE *file=fopen("data.bin","rb");
    if (file==NULL) return 1;
    if (fseek(file,0,SEEK_END)!=0) { fclose(file); return 1; }
    long size=ftell(file);
    if (size<0) { fclose(file); return 1; }
    printf("%ld\n",size);
    fclose(file);
    return 0;
}

Expected output EXAMPLE

Details

Save as snippet.c; compile with gcc -std=c17 -Wall -Wextra snippet.c -lm -o snippet, then run ./snippet. Seek to the end and inspect ftell, checking both operations for errors.

Keep in mind

This demonstrates a small ordinary seekable file on the tested Linux runtime. Streams and very large files need suitable platform APIs.

✓ Verified

Tested on Ubuntu 24.04.5 LTS · 2026-11-02 18:02:36 UTC · gcc (Ubuntu 13.3.0-6ubuntu2~24.04.1) 13.3.0 · gcc 4:13.2.0-7ubuntu1

Test inputs, results and environment

The exact published code ran in a dedicated Linux test container with prepared inputs. Unprivileged snippet process, external networking disabled, read-only root filesystem, and a fresh temporary working directory. Fixtures and output records are isolated from the application database. Testing covers this example and its stated checks, not every input, operating system, or runtime version. The Linux container shares its host's kernel; this is not a native Windows test.

Architecture / host kernel: x86_64 / 6.18.54.1-microsoft-standard-WSL2
Snippet identity / locale: uid=65534, gid=65534 (unprivileged) / C.UTF-8
Interpreter invocation: gcc -std=c17 -Wall -Wextra -Werror snippet.c -lm -o snippet && ./snippet
Container image ID: sha256:32dc2d998158b6554c99b73b533f423696a0f3e31e8cbea9db10b5eee9a2fadd
Code SHA-256: d4eeb8d6aace506188140cd99d3562e63b74965157d59b78381719093df9d4e7
Dependencies: gcc 4:13.2.0-7ubuntu1

Test input setup

These are the prepared inputs used by the test harness. See Details above for the prerequisites and how to run this example.

printf abcdef > data.bin

Observed standard output

Exit code: 0. Standard error: empty. Validation: Exact stdout comparison. System-dependent values above are one recorded run.