未定义的引用函数 [英] Undefined Reference to a function
问题描述
我使用Linux和我有以下文件:
main.c中,main.h
fileA.c,fileA.h
fileB.cpp,fileB.h
功能 F1()
在 fileB.h
声明,并在 FILEB定义的.cpp
。我需要使用的功能 fileA.c
,所以我声明了函数
的extern无效F1();
在 fileA.c
。
不过,在编译过程中,我得到了错误
fileA.c:(+的.text 0x2b7):未定义引用'F1'
什么是错的?
感谢您。
ETA:感谢我收到的答案,我现在有以下几点:
在fileA.h,我有
的#include fileB.h
#包括main.h#IFDEF __cplusplus
为externC
#万一
无效F1();
在fileA.c,我有
的#include fileA.h
在fileB.h,我有
的externC无效F1();
在fileB.cpp,我有
的#includefileB.h为externC无效F1()
{}
不过,我现在有误差
fileB.h:错误:预期的标识符或'('前字符串常量
如果你真的编译 fileA.c
为C,而不是C ++,那么你需要做确保该函数具有正确,C兼容的连接。
您可以使用的extern
关键字的一个特例做到这一点。无论是在声明和定义:
的externC无效F1();
为externC无效F1(){}
否则的C连接器会寻找一个只有真正与一些重整C ++名称存在一个功能,不支持的调用约定。 :)
不幸的是,虽然这是你必须在C ++中做什么,语法是不是在C 有效。你必须让的extern
可见只对C ++ code。
所以,一些preprocessor法宝:
的#ifdef __cplusplus
为externC
#万一
无效F1();
不完全是pretty,但它是你付出的共享两种语言的code之间的头的价格。
I'm using Linux and I have the following files:
main.c, main.h
fileA.c, fileA.h
fileB.cpp, fileB.h
The function F1()
is declared in fileB.h
and defined in fileB.cpp
. I need to use the function in fileA.c
, and so I declared the function as
extern void F1();
in fileA.c
.
However, during compilation, I got the error
fileA.c: (.text+0x2b7): undefined reference to `F1'
What is wrong?
Thank you.
ETA: Thanks to the answers I've received, I now have the following:
In fileA.h, I have
#include fileB.h
#include main.h
#ifdef __cplusplus
extern "C"
#endif
void F1();
In fileA.c, I have
#include fileA.h
In fileB.h, I have
extern "C" void F1();
In fileB.cpp, I have
#include "fileB.h"
extern "C" void F1()
{ }
However, I now have the error
fileB.h: error: expected identifier or '(' before string constant
If you're really compiling fileA.c
as C, not C++, then you need to make sure that the function has the proper, C-compatible linkage.
You can do this with a special case of the extern
keyword. Both at declaration and definition:
extern "C" void F1();
extern "C" void F1() {}
Otherwise the C linker will be looking for a function that only really exists with some mangled C++ name, and an unsupported calling convention. :)
Unfortunately, whilst this is what you have to do in C++, the syntax isn't valid in C. You must make the extern
visible only to the C++ code.
So, with some preprocessor magic:
#ifdef __cplusplus
extern "C"
#endif
void F1();
Not entirely pretty, but it's the price you pay for sharing a header between code of two languages.
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