Can we use extern in header file?

Can we use extern in header file?

The clean, reliable way to declare and define global variables is to use a header file to contain an extern declaration of the variable. The header is included by the one source file that defines the variable and by all the source files that reference the variable.

What is extern header file?

The extern keyword is used to share variables across translation units. When you declare variables in a header file, those variables are already included in the translation unit (.cpp) file that contains the header file. Therefore, any C++ file that contains “test1.h” will have internal linkage of the variable one.

What is extern function in C?

“extern” keyword is used to extend the visibility of function or variable. By default the functions are visible throughout the program, there is no need to declare or define extern functions. It just increase the redundancy. Variables with “extern” keyword are only declared not defined.

Why do we add the variable extern declaration in the .h file?

Using extern is only of relevance when the program you’re building consists of multiple source files linked together, where some of the variables defined, for example, in source file file1. c need to be referenced in other source files, such as file2. c .

How do you use extern?

the extern keyword is used to extend the visibility of variables/functions. Since functions are visible throughout the program by default, the use of extern is not needed in function declarations or definitions. Its use is implicit. When extern is used with a variable, it’s only declared, not defined.

Why do we need extern C?

Using extern “C” lets the compiler know that we want to use C naming and calling conventions. This causes the compiler to sort of entering C mode inside our C++ code. This is needed because C++ compilers mangle the names in their symbol table differently than C compilers and hence behave differently than C compilers.

What is difference between extern and global?

The extern has the word “extern” before it’s declaration, and the global doesn’t. Except when somebody is being loose with their descriptive language. There’s no real difference in what shows up in the object file or executables.

Why do we need extern in C?

Can extern variables be initialized?

You can initialize any object with the extern storage class specifier at global scope in C or at namespace scope in C++. The initializer for an extern object must either: Appear as part of the definition and the initial value must be described by a constant expression; or.

Should I use extern C?

You need to use extern “C” in C++ when declaring a function that was implemented/compiled in C. The use of extern “C” tells the compiler/linker to use the C naming and calling conventions, instead of the C++ name mangling and C++ calling conventions that would be used otherwise.

Is extern C necessary?

It’s necessary when a C++ function must be called by C code rather than C++ code. Basically, when you want your C++ library to be backwards compatible.

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