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[这个问题有关,但并不等同于这一个 ]

我的编译器警告隐式转换或将某些类型转换为bool,而显式转换不会产生警告:

long t = 0;
bool b = false;
b = t;                    // performance warning: forcing long to bool
b = (bool)t;              // performance warning
b = bool(t);              // performance warning
b = static_cast<bool>(t); // performance warning
b = t ? true : false;     // ok, no warning
b = t != 0;               // ok
b = !!t;                  // ok

这是使用Visual C++ 2008但我怀疑其他编译器可能有类似的警告.

所以我的问题是:铸造/转换的性能影响是什么bool？在某些情况下(例如,对于某些目标体系结构或处理器),显式转换是否具有更好的性能？隐式转换是否会以某种方式混淆优化器？

微软对其警告的解释并不是特别有用.他们暗示有充分的理由,但他们没有解释.