Two variables with same name and type, in two different .c files, compile with gcc

c gcc static extern
Ivan Š picture Ivan Š · Aug 25, 2011 · Viewed 9.6k times · Source

Here's the deal. I've had two identical global variables in two different .c files, they weren't declared as extern. So each .c file should have seen its own variable, right?

But I have gotten some really strange behaviour, as if one file was reading the other files variable (after linking them together). Adding 'static' qualifier to both variables definitions seemed to fix this issue.

So what I'm actually wondering is, what exactly happened there without the 'static' qualifier?

Answer

cnicutar picture cnicutar · Aug 25, 2011

So each .c file should have seen its own variable, right?

Wrong. In C, omitting static from a declaration means implicit extern linkage.

From C In a Nutshell:

The compiler treats function declarations without a storage class specifier as if they included the specifier extern. Similarly, any object identifiers that you declare outside all functions and without a storage class specifier have external linkage.

Related questions

Can I mix static and shared-object libraries when linking?

I have a C project that produces ten executables, all of which I would like to be linked in statically. The problem I am facing is that one of these executables uses a 3rd-party library of which only the shared-object …

Read More
Convert char to int in C and C++

How do I convert a char to an int in C and C++?

Read More
Debug vs Release in CMake

In a GCC compiled project, How do I run CMake for each target type (debug/release)? How do I specify debug and release C/C++ flags using CMake? How do I express that the main executable will be compiled with …

Read More