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The static keyword (static and extern are mutually exclusive), applied to the definition of an external variable, changes this a bit: the variable can only be accessed by the functions in the same module where it was defined. But it is possible for a function in the same module to pass a reference (pointer) of the variable to another function ...
A common practice for header files to maintain both C and C++ compatibility is to make its declaration be extern "C" for the scope of the header: [21] /* Header file foo.h */ #ifdef __cplusplus /* If this is a C++ compiler, use C linkage */ extern "C" { #endif /* These functions get C linkage */ void foo (); struct bar { /* ... */ }; #ifdef ...
stdarg.h is a header in the C standard library of the C programming language that allows functions to accept an indefinite number of arguments. [1] It provides facilities for stepping through a list of function arguments of unknown number and type. C++ provides this functionality in the header cstdarg.
C++ generally prohibits forward references, but they are allowed in the special case of class members. Since the member function accessor cannot be compiled until the compiler knows the type of the member variable myValue , it is the compiler's responsibility to remember the definition of accessor until it sees myValue 's declaration.
The _Thread_local (thread_local in C++, and in C since C23, and in earlier versions of C if the header <threads.h> is included) storage class specifier, introduced in C11, is used to declare a thread-local variable. It can be combined with static or extern to determine linkage.
Such extern declarations are often placed in a shared header file, since it is common practice for all .c files in a project to include at least one .h file: the standard header file errno.h is an example, making the errno variable accessible to all modules in a project.
In C99 mode, extern inline always emits a function, but like in C++, it will be shared among translation units. Thus, the same function can be defined extern inline in different translation units. [7] This matches the traditional behavior of Unix C compilers [8] for multiple non-extern definitions of uninitialized global variables.
Files intended to be included typically have a .h suffix ( .hpp or .hh are also used for C++, but .h is the most common even for C++), and generally do not contain function or variable definitions to avoid name conflicts when headers are included in multiple source files, as is often the case. Header files can be, and often are, included in ...