Implementation defined behavior control
Implementation defined behavior is controlled by
Lprefix (if any), the outer quotes, and leading/trailing whitespace from string-literal, replaces each
\, then tokenizes the result (as in translation stage 3), and then uses the result as if the input to
Pragma directive controls implementation-specific behavior of the compiler, such as disabling compiler warnings or changing alignment requirements. Any pragma that is not recognized is ignored.
 C standard pragmas
The following three pragmas are defined by the C language standard:
where arg is either
ON, informs the compiler that the program will access or modify floating-point environment, which means that optimizations that could subvert flag tests and mode changes (e.g., global common subexpression elimination, code motion, and constant folding) are prohibited. The default value is implementation-defined, usually
), and |x+iy| = √x2
, despite the possibility of intermediate overflow. In other words, the programmer guarantees that the range of the values that will be passed to those function is limited. The default value is
The behavior of the program is undefined if any of the three pragmas above appear in any context other than outside all external declarations or preceding all explicit declarations and statements inside a compound statement.