是否应在头文件或 .cpp 源文件中指定 C++ 函数默认参数值? [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*/)
{
    ...
}

这篇关于是否应在头文件或 .cpp 源文件中指定 C++ 函数默认参数值?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！