3
考虑两个以下的代码段 - 在它们之间的唯一区别是一个单一的COUT打印出值EPS:
http://ideone.com/0bEeHz - 这里的程序进入和无限循环由于COUT每股收益的变化值设为0最低双重正值 - 可以改变其价值?
#include <iostream>
int main()
{
double tmp = 1.;
double eps;
while(tmp != 0) {
eps = tmp;
tmp /= 2.;
}
if(eps == 0) {
std::cout << "(1)eps is zero!\n";
}
std::cout << "eps before: " << eps;
if(eps == 0) {
std::cout << "(2)eps is zero!\n";
}
while(eps < 1.) {
tmp = eps;
eps *= 2.;
if(tmp == eps) {
printf("wtf?\n");
}
}
std::cout << "eps after: " << eps;
}
后
http://ideone.com/pI4d30 - 这里我已经评论了cout。
#include <iostream>
int main()
{
double tmp = 1.;
double eps;
while(tmp != 0) {
eps = tmp;
tmp /= 2.;
}
if(eps == 0) {
std::cout << "(1)eps is zero!\n";
}
//std::cout << "eps before: " << eps;
if(eps == 0) {
std::cout << "(2)eps is zero!\n";
}
while(eps < 1.) {
tmp = eps;
eps *= 2.;
if(tmp == eps) {
printf("wtf?\n");
}
}
std::cout << "eps after: " << eps;
}
因此,一个单一的cout显着和令人惊讶的非常改变程序逻辑。这是为什么?
我无法在G ++ 4.7上重现这一点 – Pubby