memset, fill 对bool，int 赋值的效率

Posted 2022-03-04 thesky

memset对bool型变量赋false比对int型变量赋0快了10倍

fill对bool型变量赋false和对int型变量赋0效率一样

fill对int型变量赋0比memset对int型变量赋0慢了10倍

归结来说，以后要赋变量false的初值时，应该用bool型变量，用memset赋

#include <cstdio>
#include <cstring>
#include <ctime>
#include <algorithm>
using namespace std;

int d[2000000];
bool d2[2000000];
int has_train[1000][1000][2];
bool has_train2[1000][1000][2];

int main()

    clock_t start, finish;
    start = clock();
    int k = 1000;
    while(k--)
    
        memset(d, 0, sizeof(d));
    
    finish = clock();
    printf("%f\\n", (double)(finish - start) / CLOCKS_PER_SEC);
    start = clock();
    k = 1000;
    while(k--)
    
        memset(d2, false, sizeof(d2));
    
    finish = clock();
    printf("%f\\n", (double)(finish - start) / CLOCKS_PER_SEC);
    start = clock();
    k = 1000;
    while(k--)
    
        memset(has_train, 0, sizeof(has_train));
    
    finish = clock();
    printf("%f\\n", (double)(finish - start) / CLOCKS_PER_SEC);
    start = clock();
    k = 1000;
    while(k--)
    
        memset(has_train2, false, sizeof(has_train2));
    
    finish = clock();
    printf("%f\\n", (double)(finish - start) / CLOCKS_PER_SEC);
    
    
    
    
    
    start = clock();
    k = 1000;
    while(k--)
    
        fill(d, d+2000000, 0);
    
    finish = clock();
    printf("%f\\n", (double)(finish - start) / CLOCKS_PER_SEC);
    start = clock();
    k = 1000;
    while(k--)
    
        fill(d2, d2+2000000, false);
    
    finish = clock();
    printf("%f\\n", (double)(finish - start) / CLOCKS_PER_SEC);
    start = clock();
    k = 1000;
    while(k--)
    
        fill(has_train[0][0], has_train[0][0]+2000000, 0);
    
    finish = clock();
    printf("%f\\n", (double)(finish - start) / CLOCKS_PER_SEC);
    start = clock();
    k = 1000;
    while(k--)
    
        fill(has_train2[0][0], has_train2[0][0]+2000000, false);
    
    finish = clock();
    printf("%f\\n", (double)(finish - start) / CLOCKS_PER_SEC);
    return 0;