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Setjmp.h

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A typical use of setjmp/longjmp is implementation of an exception mechanism that exploits the ability of longjmp to reestablish program or thread state, even across multiple levels of function calls. A less common use of setjmp is to create syntax similar to coroutines.

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setjmp saves the current environment (the program state), at some point of program execution, into a platform-specific data structure (jmp_buf) that can be used at some later point of program execution by longjmp to restore the program state to that saved by setjmp into jmp_buf. This process can be imagined to be a "jump" back to the point of program execution where setjmp saved the environment. The (apparent) return value from setjmp indicates whether control reached that point normally (zero) or from a call to longjmp (nonzero). This leads to a common idiom: if( setjmp(x) ){/* handle longjmp(x) */}.

POSIX.1 does not specify whether setjmp and longjmp save and restore the current set of blocked signals; if a program employs signal handling it should use POSIX's sigsetjmp/siglongjmp.

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