pointers - C - pthread segmentation fault 11 -
i'm creating thread , passing pointer it. when cast pointer should (int*) have segmentation fault.
int *ptr = (int *)ptrtotal2; here code :
void *firstcalc(void *ptrtotal2){ int vala = 1; int valb = 2; int *ptr = (int *)ptrtotal2; *ptr = vala + valb; printf("value of vala = %d\nvalue of valb = %d\n", vala, valb); printf("value of subtotal *ptrtotal1 = %d\n", *ptr); pthread_exit(null); } int main(int argc, char **argv) { pthread_t thread1; int *ptrtotal2 = 0; int iret1; iret1 = pthread_create(&thread1, null, firstcalc, (void*) ptrtotal2); if(iret1){ fprintf(stderr,"error - pthread_create() return code: %d\n",iret1); exit(exit_failure); } pthread_join( thread1, null); exit(exit_success); }
dereferencing ptr in function firstcalc, when original pointer set 0, cause undefined behavior, in case segmentation fault.
int *ptr = (int *)ptrtotal2; *ptr = vala + valb; ... int *ptrtotal2 = 0; instead allocate memory integer, , pass created thread, , free after thread ends:
int *ptrtotal2 = malloc( sizeof( int ) ); if( !ptrtotal2 ) { abort(); } //... call pthread_create, pthread_join free( ptrtotal2 ); note, have use allocated memory (use malloc), because reading automatic variable different thread implementation defined.
6.2.4 storage durations of objects
- the result of attempting indirectly access object automatic storage duration thread other 1 object associated implementation-defined.
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