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The #pragma directive is an implementation-defined directive that allows various instructions to be given to the compiler. For example, a compiler may have an option to support the tracing of program execution. A trace option would then be specified by a #pragma statement. You must check your compiler’s documentation for the pragmas it supports.
C99 includes another way to specify a pragma in a program: the _Pragma operator. It has this general form:
_Pragma ( "directive")
Here, directive is the pragma being invoked. The _Pragma operator was added to allow pragmas to participate in macro replacement.
C99 defines the following built-in pragmas:
Pragma | Meaning |
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STDC FP_CONTRACT ON/OFF/DEFAULT | When on, floating-point expressions are treated as indivisible units that are handled by hardware-based methods. The default state is implementation defined. |
STDC FENV_ACCESS ON/OFF/DEFAULT | Tells the compiler that the floating-point environment might be accessed. The default state is implementation defined. |
STDC CX_LIMITED_RANGE ON/OFF/DEFAULT | When on, tells the compiler that certain formulas involving complex values are safe. The default state is off. |
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