C vs C++ startup cost

minimal.c

#include <stdlib.h>
#include <string.h>


const char* STR = "abcdefhijklm";

int main(int argc, char* argv[]) {
    int x = strlen("abc");
    void* v = malloc(100);
    char* s = malloc(strlen(STR));
    strcpy(s, STR);
    return 0;
}

minimal.cpp

#include <iostream>
#include <stdlib.h>
#include <string.h>
#include <string>

const char* STR = "abcdefhijklm";

int main(int argc, char* argv[]) {
    int x = strlen("abc");
    void* v = malloc(100);
    std::string s(STR);

    return 0;
}

Output

- ITERATIONS=15000
- OS: macOS 10.14.5
- Compiled using clang with -O3

Output:

running 15000 iterations for ./a.out.c
done
elapsed: 26.145948sec
1.743ms per iteration

running 15000 iterations for ./a.out.cpp
done
elapsed: 26.000413sec
1.733ms per iteration

timer.cpp

#include <spawn.h>
#include <string.h>
#include <sys/time.h>
#include <sys/wait.h>
#include <unistd.h>

#define ITERATIONS 1000

int spawnloop(const char* prog, char *envp[]) {

    timeval start_time;
    timeval end_time;

    printf("running %d iterations for %s\n", ITERATIONS, prog);
    gettimeofday(&start_time, NULL);

    char* child_argv[] = {NULL};
    for (int i = 0; i < ITERATIONS; i++) {
        int err = -1;
        pid_t child_pid = -1;
        err = posix_spawn(
            &child_pid,
            prog,
            NULL,
            NULL,
            child_argv,
            envp
        );
        if (err != 0) {
            printf("error %d (%s) @ iteration %d", err, strerror(err), i);
            return 1;
        }
        int waitstatus;
        waitpid(child_pid, &waitstatus, 0);
    }

    gettimeofday(&end_time, NULL);
    printf("done\n");

    timeval diff_time;
    timersub(&end_time, &start_time, &diff_time);

    double elapsed_usec = (diff_time.tv_sec*1000*1000 + diff_time.tv_usec);
    printf("elapsed: %.6lfsec\n", elapsed_usec / 1000/1000);

    double ms_per_iteration = elapsed_usec / (1000.0 * ITERATIONS);
    printf("%.3lfms per iteration\n", ms_per_iteration);
    printf("\n");
    return 0;
}

int main(int argc, char* argv[], char* envp[]) {
    int a = spawnloop("./a.out.c", envp);
    sleep(3);
    int b = spawnloop("./a.out.cpp", envp);
    return a ? a : b;
}