Barebones library in C for timing things (uses POSIX time definition for counting elapsed seconds and milliseconds)

stopwatch.c

#include "stopwatch.h"
#include <sys/time.h>
#include <stdlib.h>

struct stop_watch {
    struct timeval start;
    struct timeval end;
};

Stopwatch stopwatch_create() {
    return calloc(1, sizeof(struct stop_watch));
}

void stopwatch_start(Stopwatch s) {
    gettimeofday(&(s->start), NULL);
}

void stopwatch_stop(Stopwatch s) {
    gettimeofday(&(s->end), NULL);
}

long stopwatch_seconds(Stopwatch s) {
    return s->end.tv_sec - s->start.tv_sec;
}

long stopwatch_microseconds(Stopwatch s) {
    return s->end.tv_usec - s->start.tv_usec;
}

stopwatch.h

#ifndef STOPWATCH_H
#define STOPWATCH_H

// Define the Stopwatch as the object (pointer to struct)
struct stop_watch;
typedef struct stop_watch* Stopwatch;

// Returns a newly allocated Stopwatch object
Stopwatch stopwatch_create();

// Triggers the Stopwatch object to start or stop
void stopwatch_start(Stopwatch s);
void stopwatch_stop(Stopwatch s);

// Grab the number of seconds or microseconds that have elapsed on this Stopwatch
// WARNING: if stopwatch_start() and stopwatch_stop() are not both called in that order, behavior is not guaranteed
long stopwatch_seconds(Stopwatch s);
long stopwatch_microseconds(Stopwatch s);

#endif