是否应在标头或.cpp源文件中指定C ++函数的默认参数值？ [英] Should C++ function default argument values be specified in headers or .cpp source files?

问题描述

我是C ++的新手。我在设置标题时遇到了麻烦。这是来自functions.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中使用它的方式。 cpp

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不会知道最后一个参数是可选的。我该如何进行这项工作？

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

您进行声明（即在头文件中- functions .h ）包含可选参数，而不包含定义（ 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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