小编A.H*_*tov的帖子

假设我们有一个 A 类：

template<int N>
class A final{
public:
    void foo() const { cout << N << endl; }
};

模板参数 N 存储在哪里？在堆中还是在堆栈中的对象内存中？

我有一个非常简单的程序来测量一个函数花费了多少时间。

#include <iostream>
#include <vector>
#include <chrono>
struct Foo
{
    void addSample(uint64_t s)
    {
    }
};

void test(const std::vector<uint64_t>& samples)
{
    uint32_t onlyCallTime = 0;
    uint32_t loopOnlyTime = 0;
    Foo stats;
    std::chrono::high_resolution_clock::time_point callStart,callEnd;
    auto start = callStart = callEnd = std::chrono::high_resolution_clock::now();
    for(auto &s : samples)
    {
        callStart = std::chrono::high_resolution_clock::now();
        loopOnlyTime += std::chrono::duration_cast<std::chrono::microseconds>(callStart-callEnd).count();
        stats.addSample(s);
        callEnd = std::chrono::high_resolution_clock::now();
        onlyCallTime += std::chrono::duration_cast<std::chrono::microseconds>(callEnd-callStart).count();
    }
    auto end = std::chrono::high_resolution_clock::now();

    std::cout << "overall duration: " << std::chrono::duration_cast<std::chrono::microseconds>(end-start).count() << std::endl;
    std::cout << "only call duration: " << …

So I was messing around with inline assembly and compiled this using GCC 9. The result was that the two variables a and b were swapped without actually issuing any direct commands.

#include<cstdio>
int main(){
    int a(1),b(2),c(3);
    asm ("": "=r"(c):"r"(a));
    asm ("": "=r"(a):"r"(b));
    asm ("": "=r"(b):"r"(c));
    printf("%d %d %d", a,b,c);
}

Can somebody explain what is going on here?