是否应在头文件或 .cpp 源文件中指定 C++ 函数默认参数值?
我对 C++ 有点陌生.我在设置标题时遇到问题.这是来自函数.h
I am kind of new to C++. I am having trouble setting up my headers. This is from functions.h
extern void apply_surface(int, int, SDL_Surface *, SDL_Surface *,SDL_Rect *);
这是来自functions.cpp的函数定义
And this is the function definition from functions.cpp
void
apply_surface(int x, int y, SDL_Surface * source, SDL_Surface *
destination,SDL_Rect *clip = NULL)
{
...
}
这就是我在 main.cpp 中使用它的方式
And this is how I use it in main.cpp
#include "functions.h"
int
main (int argc, char * argv[])
{
apply_surface(bla,bla,bla,bla); // 4 arguments, since last one is optional.
}
但是，这不会编译，因为 main.cpp 不知道最后一个参数是可选的.我怎样才能做到这一点?
But, this doesn't compile, because, main.cpp doesn't know last parameter is optional. How can I make this work?
推荐答案
您使声明(即在头文件 - functions.h 中)包含可选参数，而不是定义(functions.cpp).
You make the declaration (i.e. in the header file - functions.h) contain the optional parameter, not the definition (functions.cpp).
//functions.h
extern void apply_surface(int, int, SDL_Surface *, SDL_Surface *,SDL_Rect * clip = NULL);
//functions.cpp
void apply_surface(int x, int y, SDL_Surface * source, SDL_Surface *
destination,SDL_Rect *clip /*= NULL*/)
{
...
}
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