memory allocation performance

zero.cpp

#include <cstring>
#include <cmath>
#include <cstdio>
#include <ctime>
#include <cstdlib>
#include <vector>
#define NITER 100//5000000

int main() {
    clock_t t;

    t = clock();
    for(size_t i = 0; i < NITER; i++) {
        char* buf = (char*)malloc(8*1024*1024);
        asm volatile ("" :: "g"(buf) : "memory");
        free(buf);        
    }
    printf("pure %fs\n", float(clock() - t)/CLOCKS_PER_SEC);

    t = clock();
    for(size_t i = 0; i < NITER; i++) {
        char* buf = (char*)malloc(8*1024*1024);
        memset(buf, buf[0], 8*1024*1024);
        asm volatile ("" :: "g"(buf) : "memory");
        free(buf);        
    }
    printf("memset %fs\n", float(clock() - t)/CLOCKS_PER_SEC);

    t = clock();
    std::vector<char> buf;
    for(size_t i = 0; i < NITER; i++) {
        buf.resize(8*1024*1024);
        asm volatile ("" :: "g"(&buf[0]) : "memory");  
        buf.clear();
    }
    printf("vector %fs\n", float(clock() - t)/CLOCKS_PER_SEC);

    return 0;
}