Define global variable to use in multiple source files

Question

I have a variable that I intend to use in multiple files, is a mutex initializer.

So I wrote in one header file this :

#ifndef LISTEN_H_
#define LISTEN_H_

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

#endif

I tried to include the header in the files in witch I intend to use the variable.

But i get : error mutex has already been declared here.

What is the proper way to use a global variable in multiple header files ?

Karthik T · Accepted Answer · 2013-03-01 08:38:47Z

6

The proper way would be to define it in a .c file and declare it as extern in the header file. Now you would be able to use it wherever you want to use it, without errors.

answered Mar 1, 2013 at 8:38

Karthik T

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4 Comments

Jeegar Patel Over a year ago

then whats the purpose of header guard..?

Karthik T Over a year ago

@Mr.32 the include guard prevents the file from being included multiple times IN THE SAME translation unit - i.e during compilation.

Karthik T Over a year ago

@Mr.32 This error, is due to multiple copies of the variables defined in different translation units - during linking stage.

Jeegar Patel Over a year ago

@KarthikT oh OP hasnt specify that in question still u get it..great +1

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