c++ 获取数字字符串的子串数值性能示例分析

#include <string>
#include <iostream>
#include <chrono>
using namespace std;
int main(int argc, char* argv[]) {
    string val = "123";
    int total = 1000000;
    std::chrono::time_point<std::chrono::system_clock> start = std::chrono::system_clock::now();
    for (int i = 0; i < total; i++) {
        int tmp = atoi(val.substr(1, 2).c_str());
    }
    std::chrono::time_point<std::chrono::system_clock> end = std::chrono::system_clock::now();
    std::chrono::microseconds diff = std::chrono::duration_cast<std::chrono::microseconds>(end - start);
    cout << "using substr:" << diff.count() << "ms" << endl;
    start = std::chrono::system_clock::now();
    for (int i = 0; i < total; i++) {
        char vals[2] = { val[1],val[2] };
        int tmp = atoi(vals);
    }
    end = std::chrono::system_clock::now();
    diff = std::chrono::duration_cast<std::chrono::microseconds>(end - start);
    cout << "using char[]:" << diff.count() << "ms" << endl;
    return 0;
}