55_pdfsam_cs2022

55_pdfsam_cs2022 - Local variables Recall that local...

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Local variables Recall that local variables are stored on the stack Memory for local variables is deallocated when function returns Returning a pointer to a local variable is almost always a bug! C requires that the size of variables on the stack be known at compile time, so dynamically-sized arrays aren’t possible char *my_strcat(char *s1, char *s2) { char s3[1024]; strcpy(s3, s1); strcat(s3, s2); return s3; // BUG! returns a pointer to a // deallocated memory region. }
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The Heap C can use space in another part of memory: the heap The heap is separate from the execution stack Heap regions are not deallocated when a function returns Note: this is completely unrelated to the Heap data structure The programmer requests storage space on the heap C never puts variables on the heap automatically But local variables might point to locations on the heap Heap space must be explicitly allocated and deallocated by the programmer
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malloc Library function in stdlib.h
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