检查混合 C/C++ 中是否定义了 bool
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Check if bool is defined in mixed C/C++
提问by prelic
So I'm having issues with some code that I've inherited. This code was building fine in a C-only environment, but now I need to use C++ to call this code. The header problem.hcontains:
所以我在继承一些代码时遇到了问题。这段代码在纯 C 环境中构建得很好，但现在我需要使用 C++ 来调用这段代码。标题problem.h包含：
#ifndef _BOOL
typedef unsigned char bool;
static const bool False = 0;
static const bool True = 1;
#endif
struct astruct
{
bool myvar;
/* and a bunch more */
}
When I compile it as C++ code, I get error C2632: 'char' followed by 'bool' is illegal
当我将它编译为 C++ 代码时，我得到 error C2632: 'char' followed by 'bool' is illegal
I get the same error if I wrap the #include "problem.h"in extern "C" { ... }(which I don't understand, because there should be no keyword boolwhen compiling as C?)
如果我将#include "problem.h"in包装起来，我会得到同样的错误extern "C" { ... }（我不明白，因为bool编译为 C 时应该没有关键字？）
I tried removing the block from #ifndef _BOOLto #endif, and compiling as C++, and I get errors:
我尝试从#ifndef _BOOLto 中删除块#endif，并编译为 C++，但出现错误：
error C2061: C requires that a struct or union has at least one membererror C2061: syntax error: identifier 'bool'
error C2061: C requires that a struct or union has at least one membererror C2061: syntax error: identifier 'bool'
I just don't understand how the C++ compiler is complaining about a redefinition of bool, yet when I remove the redefinition and try to just use boolto define variables, it doesn't find anything.
我只是不明白 C++ 编译器如何抱怨 的重定义bool，但是当我删除重定义并尝试仅用于bool定义变量时，它没有找到任何东西。
Any help is greatly appreciated.
任何帮助是极大的赞赏。
回答by Luchian Grigore
Because boolis a basic type in C++ (but not in C), and can't be redefined.
因为bool是 C++ 中的基本类型（但不是 C），并且不能重新定义。
You can surround your code with
你可以用你的代码包围
#ifndef __cplusplus
typedef unsigned char bool;
static const bool False = 0;
static const bool True = 1;
#endif
回答by Richard J. Ross III
You can use C99's bool:
您可以使用 C99 的bool：
#ifndef __cplusplus
#include <stdbool.h>
#endif
bool myBoolean; // bool is declared as either C99's _Bool, or C++'s bool data type.
Why should you use this?
为什么要使用这个？
For compatibility with other C99 code. _Boolis commonly used in C99 Code, and is very useful. It also grants you the ability to have a boolean datatype without the need to typedef a lot of stuff, as behind the scenes, _Boolis a datatype defined by the compiler.
与其他 C99 代码兼容。_Bool常用在C99代码中，非常有用。它还使您能够拥有布尔数据类型，而无需 typedef 很多东西，因为在幕后，_Bool是由编译器定义的数据类型。
回答by Component 10
You should use the __cplusplusmacro:
您应该使用__cplusplus宏：
#ifndef __cplusplus
#ifndef _BOOL
typedef unsigned char bool;
static const bool False = 0;
static const bool True = 1;
#endif
#endif
Check out this link to the C++ FAQfor further details.
查看C++ 常见问题的链接以获取更多详细信息。
回答by Justin Hirsch
I had this "'char' followed by 'bool' is illegal" problem in VS also. The problem for me was I did not end my class declaration with a semi-colon- which I was not expecting to be the issue as this was in the header file and the problem was coming up in the cpp file! eg:
我在VS中也有这个“'char'后跟'bool'是非法的”问题。我的问题是我没有用分号结束我的类声明 - 我没想到这是问题，因为这是在头文件中，而问题出现在 cpp 文件中！例如：
class myClass
{
}; // <-- put the semi colon !!
