[英]Why can't a class method call a global function with the same name?
The following code shows a function call another function. 以下代码显示了一个函数调用另一个函数。
Both have the same name, but different signatures. 两者名称相同,但签名不同。
This works as expected. 这按预期工作。
//declarations
void foo();
void foo(int);
int main(){
foo();
}
//definitions
void foo(){
foo(1);
}
void foo(int){}
The only difference I will make now, is wrap one of the functions into a structure: 我现在唯一要做的就是将其中一个函数包装到一个结构中:
//declarations
struct Bar{
void foo();
};
void foo(int);
int main(){
Bar bar;
bar.foo();
}
//definitions
void Bar::foo(){
foo(1);
}
void foo(int){}
This fails to compile. 这无法编译。
In member function ‘void Bar::foo()’:
error: no matching function for call to ‘Bar::foo(int)’
foo(1);
^
note: candidate: void Bar::foo()
void Bar::foo(){
^
note: candidate expects 0 arguments, 1 provided
I don't understand why it wants to call foo(int) as a method, when the global function exists. 当全局函数存在时,我不明白为什么它要调用foo(int)作为方法。
It doesn't mention anything about ambiguity, it just can't find the function. 它没有提及任何歧义,只是找不到函数。
Why is this happening, and how can I fix it? 为什么会发生这种情况,我该如何解决?
side note: I'm wrapping old C code in a C++ wrapper, and most of the C++ methods are calls to the global C functions which pass in the wrapped struct implicitly. 旁注:我将旧的C代码包装在C ++包装器中,并且大多数C ++方法都是对全局C函数的调用,这些函数隐式地传递包装的结构。 It's a similar situation to what is happening above (in terms of compiler errors). 这与上面发生的情况类似(就编译器错误而言)。
The member function is hiding the global. 成员函数隐藏全局。 It finds the name in the class context, therefore it not continue to search it in other contexts. 它在类上下文中找到该名称,因此不会在其他上下文中继续搜索它。
You need to call it like this: 您需要这样称呼它:
::foo(1);
Another solution is to use forward declaration inside the function, like this: 另一个解决方案是在函数内部使用前向声明,如下所示:
void Bar::foo()
{
void foo(int);
foo(1);
}
As Praetorian suggests, here is another option: 正如Praetorian所建议的,这是另一种选择:
void Bar::foo()
{
using ::foo;
foo(1);
}
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