C++ 多重定义首先在这里定义gcc
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Multiple definition of first defined here gcc
提问by Some programmer dude
I have these files
我有这些文件
consumer.cpp
consumer.hpp
defines.hpp
main.cpp
makefile
producer.cpp
producer.hpp
here's the file defines.hpp
这是文件defines.hpp
#ifndef DEFINES_HPP
#define DEFINES_HPP
#include <cassert>
#include <pthread.h>
#include <queue>
#include <stdlib.h>
#include <string>
#include <unistd.h>
pthread_mutex_t set_queue_mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t condition_var = PTHREAD_COND_INITIALIZER;
std::queue<int> q;
#endif // DEFINES_HPP
This defines.hpp file is included in the producer.hpp and consumer.hpp. producer.hpp and consumer.hpp files respectively included to producer.cpp and consumer.cpp and yet to main.cpp. When compiling I get an error.
这个defines.hpp 文件包含在producer.hpp 和consumer.hpp 中。producer.hpp 和consumer.hpp 文件分别包含在producer.cpp 和consumer.cpp 中，但尚未包含在main.cpp 中。编译时出现错误。
g++ -o main producer.cpp consumer.cpp main.cpp producer.hpp consumer.hpp defines.hpp -lpthread -ggdb
/tmp/ccctuRp7.o: In function `__gnu_cxx::new_allocator<int>::destroy(int*)':
/home/vardan/test/consumer.cpp:8: multiple definition of `set_queue_mutex'
/tmp/cciGccft.o:/home/vardan/test/producer.cpp:8: first defined here
/tmp/ccctuRp7.o: In function `std::deque<int, std::allocator<int> >::front()':
/home/vardan/test/consumer.cpp:12: multiple definition of `condition_var'
/tmp/cciGccft.o:/home/vardan/test/producer.cpp:11: first defined here
/tmp/ccctuRp7.o: In function `global::consumer::entry_point(void*)':
/home/vardan/test/consumer.cpp:17: multiple definition of `q'
/tmp/cciGccft.o:/home/vardan/test/producer.cpp:17: first defined here
/tmp/ccKCxptM.o: In function `main':
/home/vardan/test/main.cpp:8: multiple definition of `set_queue_mutex'
/tmp/cciGccft.o:/home/vardan/test/producer.cpp:8: first defined here
/tmp/ccKCxptM.o: In function `main':
/home/vardan/test/main.cpp:13: multiple definition of `condition_var'
/tmp/cciGccft.o:/home/vardan/test/producer.cpp:11: first defined here
/tmp/ccKCxptM.o: In function `main':
/home/vardan/test/main.cpp:25: multiple definition of `q'
/tmp/cciGccft.o:/home/vardan/test/producer.cpp:17: first defined here
collect2: error: ld returned 1 exit status
make: *** [main] Error 1
Here is my makefile
这是我的makefile
main : producer.cpp consumer.cpp main.cpp producer.hpp consumer.hpp defines.hpp
g++ -o $@ $^ -lpthread -ggdb
.PHONY : clean
clean:
rm -rf main *.swf *.o
How to solve this problem ?
如何解决这个问题呢 ？
回答by Some programmer dude
In C++ (as well as in C) there is a difference between declaringand definingthings like variables. What you are doing in the header file is definingthe variables, which means that every source file that includes the header file will have the definitions.
在 C++（以及 C）中，声明和定义诸如变量之类的东西是有区别的。您在头文件中所做的是定义变量，这意味着每个包含头文件的源文件都将具有定义。
In the header file you should only declarethe variables, and then in a single source file define them.
在头文件中你应该只声明变量，然后在一个源文件中定义它们。
So in the header file do e.g.
所以在头文件中做例如
extern pthread_mutex_t set_queue_mutex;
extern pthread_cond_t condition_var;
extern std::queue<int> q;
And then in a single source file put the definitions (what you have now).
然后在单个源文件中放置定义（您现在拥有的）。
