Other Builtins (Using the GNU Compiler Collection (GCC))

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2024-11-22 14:00:21

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GCC provides a large number of built-in functions other than the ones mentioned above. Some of these are for internal use in the processing of exceptions or variable-length argument lists and are not documented here because they may change from time to time; we do not recommend general use of these functions.

With the exception of built-ins that have library equivalents such as the standard C library functions discussed below, or that expand to library calls, GCC built-in functions are always expanded inline and thus do not have corresponding entry points and their address cannot be obtained. Attempting to use them in an expression other than a function call results in a compile-time error.

GCC includes built-in versions of many of the functions in the standard C library. These functions come in two forms: one whose names start with the __builtin_ prefix, and the other without. Both forms have the same type (including prototype), the same address (when their address is taken), and the same meaning as the C library functions even if you specify the -fno-builtin option see Options Controlling C Dialect). Many of these functions are only optimized in certain cases; if they are not optimized in a particular case, a call to the library function is emitted.