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man pages section 2: System Calls

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Updated: Wednesday, July 27, 2022



getcontext, setcontext - get and set current user context


#include <ucontext.h>

int getcontext(ucontext_t *ucp);
int setcontext(const ucontext_t *ucp);


The getcontext() function initializes the structure pointed to by ucp to the current user context of the calling process. The ucontext_t type that ucp points to defines the user context and includes the contents of the calling process' machine registers, the signal mask, and the current execution stack.

The setcontext() function restores the user context pointed to by ucp. A successful call to setcontext() does not return; program execution resumes at the point specified by the ucp argument passed to setcontext(). The ucp argument should be created either by a prior call to getcontext(), or by being passed as an argument to a signal handler. If the ucp argument was created with getcontext(), program execution continues as if the corresponding call of getcontext() had just returned. If the ucp argument was created with makecontext(3C), program execution continues with the function passed to makecontext(3C). When that function returns, the process continues as if after a call to setcontext() with the ucp argument that was input to makecontext(3C). If the ucp argument was passed to a signal handler, program execution continues with the program instruction following the instruction interrupted by the signal. If the uc_link member of the ucontext_t structure pointed to by the ucp argument is equal to 0, then this context is the main context, and the process will exit when this context returns. The effects of passing a ucp argument obtained from any other source are unspecified.

Return Values

On successful completion, setcontext() does not return and getcontext() returns 0. Otherwise, −1 is returned.


No errors are defined.


Portable applications should not modify or access the uc_mcontext member of ucontext_t. A portable application cannot assume that context includes any process-wide static data, possibly including errno. Users manipulating contexts should take care to handle these explicitly when required.


See attributes(7) for descriptions of the following attributes:

Interface Stability

See Also

sigaction(2), sigaltstack(2), sigprocmask(2), bsd_signal(3C), makecontext(3C), ucontext.h(3HEAD), attributes(7), standards(7)