C编译时`true' undeclared (first use in this function)
2017-10-30 17:13
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在编译C语言时有时会遇到这样的错误提示:
`true' undeclared (first use in this function) or `false' undeclared (first use in this function)
就是说 bool, true, false 都是undeclared,原因很简单,因为真正的C中没有这些关键字,c和早期的c++里没有关键字bool,使用BOOL可以,但BOOL不是内置类型了,都是通过typedef或者宏来定义的,通常都会被定义成int类型。后来的c++出现了内置类型bool,值只能为true(1)和false(0)。
解决方法:
1、将文件名.c改为文件名.cpp,用C++方式编译则没问题
2、自己进行一个宏定义:
typedef enum __bool { false = 0, true = 1, } bool;
c90是没有bool的,因此支持c90的dev-c++当然也没有。想在c90里用bool,可以自行用宏进行定义。
c99支持bool,用支持c99的编译器例如gcc就可以的。
`true' undeclared (first use in this function) or `false' undeclared (first use in this function)
就是说 bool, true, false 都是undeclared,原因很简单,因为真正的C中没有这些关键字,c和早期的c++里没有关键字bool,使用BOOL可以,但BOOL不是内置类型了,都是通过typedef或者宏来定义的,通常都会被定义成int类型。后来的c++出现了内置类型bool,值只能为true(1)和false(0)。
解决方法:
1、将文件名.c改为文件名.cpp,用C++方式编译则没问题
2、自己进行一个宏定义:
typedef enum __bool { false = 0, true = 1, } bool;
c90是没有bool的,因此支持c90的dev-c++当然也没有。想在c90里用bool,可以自行用宏进行定义。
c99支持bool,用支持c99的编译器例如gcc就可以的。
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