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[2] [3] [4] When conditional compilation is done via a preprocessor that does not guarantee syntactically correct output in the source language, such as the C preprocessor, this may lead to hard-to-debug compilation errors, [5] [6] [7] which is sometimes called "#ifdef hell." [8] [9]
One little-known usage pattern of the C preprocessor is known as X-Macros. [5] [6] [7] An X-Macro is a header file. Commonly, these use the extension .def instead of the traditional .h. This file contains a list of similar macro calls, which can be referred to as "component macros." The include file is then referenced repeatedly.
For #include guards to work properly, each guard must test and conditionally set a different preprocessor macro. Therefore, a project using #include guards must work out a coherent naming scheme for its include guards, and make sure its scheme doesn't conflict with that of any third-party headers it uses, or with the names of any globally visible macros.
The One Definition Rule (ODR) is an important rule of the C++ programming language that prescribes that classes/structs and non-inline functions cannot have more than one definition in the entire program and templates and types cannot have more than one definition by translation unit.
C++ began as a fork of an early, pre-standardized C, and was designed to be mostly source-and-link compatible with C compilers of the time. [1] [2] Due to this, development tools for the two languages (such as IDEs and compilers) are often integrated into a single product, with the programmer able to specify C or C++ as their source language.
In the C and C++ programming languages, an inline function is one qualified with the keyword inline; this serves two purposes: . It serves as a compiler directive that suggests (but does not require) that the compiler substitute the body of the function inline by performing inline expansion, i.e. by inserting the function code at the address of each function call, thereby saving the overhead ...