请教C++和C混合编程问题

石下醉客

有三个文件，使用了大数库GMP
test.h

1. #include <gmp.h>
   
2. #include <stdio.h>
   
3. void print_msg(mpz_t message);

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test.c

1. #include "test.h"
   
2. #include <stdio.h>
   
3. 
   
4. void print_msg(mpz_t message)
   
5. {
   
6.         mpz_out_str(stderr, 10, message);
   
7.         fputs("\n", stderr);
   
8. }

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main.cpp

1. #include "test.h"
   
2. #include <stdio.h>
   
3. 
   
4. int main()
   
5. {
   
6.         mpz_t message;
   
7.         mpz_init(message);
   
8.         mpz_set_ui(message, 100)
   
9.         print_msg(message);
   
10.         return 0;
    
11. }

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Makefile

1. CC = g++
   
2. CFLAGS = -Wall -I/usr/local/include/
   
3. LDFLAGS = -lgmp
   
4. 
   
5. all: main
   
6. 
   
7. test.o: test.c
   
8.         $(CC) -c -g -o $@ $^ $(CFLAGS)
   
9. 
   
10. main.o: main.cpp
    
11.         $(CC) -c -g -o $@ $^ $(CFLAGS)
    
12. 
    
13. main: test.o main.o
    
14.         $(CC) -o $@ $^ $(LDFLAGS)
    
15. 
    
16. clean:
    
17.         rm -f *.o test main

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在C++中调用C文件。这样会出现链接失败，也就是"unreference to print_msg”，于是把main.cpp改成

1. extern "C"
   
2. {
   
3. #include "test.h"
   
4. }
   
5. #include <stdio.h>
   
6. 
   
7. int main()
   
8. {
   
9.         mpz_t message;
   
10.         mpz_init(message);
    
11.         mpz_set_ui(message, 100L);
    
12.         print_msg(message);
    
13. 
    
14.         return 0;
    
15. }

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但是编译会出现如下错误
g++ -c -g -o test.o test.c -Wall -I/usr/local/include/
g++ -c -g -o main.o main.cpp -Wall -I/usr/local/include/  
In file included from /usr/include/c++/4.8/bits/stringfwd.h:40:0,
                 from /usr/include/c++/4.8/iosfwd:39,
                 from /usr/local/include/gmp.h:34,
                 from test.h:1,
                 from main.cpp:3:
/usr/include/c++/4.8/bits/memoryfwd.h:63:3: error: template with C linkage
   template<typename>
   ^
/usr/include/c++/4.8/bits/memoryfwd.h:66:3: error: template specialization with C linkage
   template<>
   ^
/usr/include/c++/4.8/bits/memoryfwd.h:70:3: error: template with C linkage
   template<typename, typename>
   ^
In file included from /usr/include/c++/4.8/iosfwd:39:0,
                 from /usr/local/include/gmp.h:34,
                 from test.h:1,
                 from main.cpp:3:
/usr/include/c++/4.8/bits/stringfwd.h:52:3: error: template with C linkage
   template<class _CharT>
   ^
/usr/include/c++/4.8/bits/stringfwd.h:55:3: error: template with C linkage
   template<typename _CharT, typename _Traits = char_traits<_CharT>,
   ^
/usr/include/c++/4.8/bits/stringfwd.h:59:3: error: template specialization with C linkage
   template<> struct char_traits<char>;
   ^
/usr/include/c++/4.8/bits/stringfwd.h:65:3: error: template specialization with C linkage
   template<> struct char_traits<wchar_t>;
   ^
In file included from /usr/include/c++/4.8/iosfwd:40:0,
                 from /usr/local/include/gmp.h:34,
                 from test.h:1,
                 from main.cpp:3:
/usr/include/c++/4.8/bits/postypes.h:111:3: error: template with C linkage
   template<typename _StateT>
   ^
/usr/include/c++/4.8/bits/postypes.h:214:3: error: template with C linkage
   template<typename _StateT>
   ^
/usr/include/c++/4.8/bits/postypes.h:219:3: error: template with C linkage
   template<typename _StateT>
   ^
In file included from /usr/local/include/gmp.h:34:0,
                 from test.h:1,
                 from main.cpp:3:
/usr/include/c++/4.8/iosfwd:76:3: error: template with C linkage
   template<typename _CharT, typename _Traits = char_traits<_CharT> >
   ^
/usr/include/c++/4.8/iosfwd:79:3: error: template with C linkage
   template<typename _CharT, typename _Traits = char_traits<_CharT> >
   ^
/usr/include/c++/4.8/iosfwd:82:3: error: template with C linkage
   template<typename _CharT, typename _Traits = char_traits<_CharT> >
   ^
/usr/include/c++/4.8/iosfwd:85:3: error: template with C linkage
   template<typename _CharT, typename _Traits = char_traits<_CharT> >
   ^
/usr/include/c++/4.8/iosfwd:88:3: error: template with C linkage
   template<typename _CharT, typename _Traits = char_traits<_CharT> >
   ^
/usr/include/c++/4.8/iosfwd:91:3: error: template with C linkage
   template<typename _CharT, typename _Traits = char_traits<_CharT>,
   ^
/usr/include/c++/4.8/iosfwd:95:3: error: template with C linkage
   template<typename _CharT, typename _Traits = char_traits<_CharT>,
   ^
/usr/include/c++/4.8/iosfwd:99:3: error: template with C linkage
   template<typename _CharT, typename _Traits = char_traits<_CharT>,
   ^
/usr/include/c++/4.8/iosfwd:103:3: error: template with C linkage
   template<typename _CharT, typename _Traits = char_traits<_CharT>,
   ^
/usr/include/c++/4.8/iosfwd:107:3: error: template with C linkage
   template<typename _CharT, typename _Traits = char_traits<_CharT> >
   ^
/usr/include/c++/4.8/iosfwd:110:3: error: template with C linkage
   template<typename _CharT, typename _Traits = char_traits<_CharT> >
   ^
/usr/include/c++/4.8/iosfwd:113:3: error: template with C linkage
   template<typename _CharT, typename _Traits = char_traits<_CharT> >
   ^
/usr/include/c++/4.8/iosfwd:116:3: error: template with C linkage
   template<typename _CharT, typename _Traits = char_traits<_CharT> >
   ^
/usr/include/c++/4.8/iosfwd:119:3: error: template with C linkage
   template<typename _CharT, typename _Traits = char_traits<_CharT> >
   ^
/usr/include/c++/4.8/iosfwd:122:3: error: template with C linkage
   template<typename _CharT, typename _Traits = char_traits<_CharT> >
   ^
In file included from test.h:1:0,
                 from main.cpp:3:
/usr/local/include/gmp.h:2251:71: error: declaration of C function ‘std:stream& operator<<(std:stream&, mpq_srcptr)’ conflicts with
__GMP_DECLSPEC_XX std:stream& operator<< (std:stream &, mpq_srcptr);
                                                                       ^
/usr/local/include/gmp.h:2250:33: error: previous declaration ‘std:stream& operator<<(std:stream&, mpz_srcptr)’ here
__GMP_DECLSPEC_XX std:stream& operator<< (std:stream &, mpz_srcptr);
                                 ^
/usr/local/include/gmp.h:2252:71: error: declaration of C function ‘std:stream& operator<<(std:stream&, mpf_srcptr)’ conflicts with
__GMP_DECLSPEC_XX std::ostream& operator<< (std::ostream &, mpf_srcptr);
                                                                       ^
/usr/local/include/gmp.h:2251:33: error: previous declaration ‘std::ostream& operator<<(std::ostream&, mpq_srcptr)’ here
__GMP_DECLSPEC_XX std::ostream& operator<< (std::ostream &, mpq_srcptr);
                                 ^
/usr/local/include/gmp.h:2252:71: error: declaration of C function ‘std::ostream& operator<<(std::ostream&, mpf_srcptr)’ conflicts with
__GMP_DECLSPEC_XX std::ostream& operator<< (std::ostream &, mpf_srcptr);
                                                                       ^
/usr/local/include/gmp.h:2250:33: error: previous declaration ‘std::ostream& operator<<(std::ostream&, mpz_srcptr)’ here
__GMP_DECLSPEC_XX std::ostream& operator<< (std::ostream &, mpz_srcptr);
                                 ^
/usr/local/include/gmp.h:2254:68: error: declaration of C function ‘std::istream& operator>>(std::istream&, mpq_ptr)’ conflicts with
__GMP_DECLSPEC_XX std::istream& operator>> (std::istream &, mpq_ptr);
                                                                    ^
/usr/local/include/gmp.h:2253:33: error: previous declaration ‘std::istream& operator>>(std::istream&, mpz_ptr)’ here
__GMP_DECLSPEC_XX std::istream& operator>> (std::istream &, mpz_ptr);
                                 ^
/usr/local/include/gmp.h:2255:68: error: declaration of C function ‘std::istream& operator>>(std::istream&, mpf_ptr)’ conflicts with
__GMP_DECLSPEC_XX std::istream& operator>> (std::istream &, mpf_ptr);
                                                                    ^
/usr/local/include/gmp.h:2254:33: error: previous declaration ‘std::istream& operator>>(std::istream&, mpq_ptr)’ here
__GMP_DECLSPEC_XX std::istream& operator>> (std::istream &, mpq_ptr);
                                 ^
/usr/local/include/gmp.h:2255:68: error: declaration of C function ‘std::istream& operator>>(std::istream&, mpf_ptr)’ conflicts with
__GMP_DECLSPEC_XX std::istream& operator>> (std::istream &, mpf_ptr);
                                                                    ^
/usr/local/include/gmp.h:2253:33: error: previous declaration ‘std::istream& operator>>(std::istream&, mpz_ptr)’ here
__GMP_DECLSPEC_XX std::istream& operator>> (std::istream &, mpz_ptr);
                                 ^
make: *** [main.o] 错误 1

hellioncu

test.h 改成

#include <gmp.h>
#include <stdio.h>

#ifdef __cplusplus
extern "C" {
#endif

void print_msg(mpz_t message);

#ifdef __cplusplus
}
#endif

hanxin83

同意楼上, 虽然不知道gmp是嘛玩意, 但看错误感觉它是c++写的...

zsszss0000

编译gcc源代码的时候就会用到这个库回复 3# hanxin83