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crestrict-qualifierstrtol

Aliased arguments in strtol

Here is how strtol has to be declared according to § 7.22.1.4 from C11 (n1570):

#include <stdlib.h>

long int strtol (const char *restrict nptr,
                 char **restrict endptr,
                 int base);

As far as I know, the restrict keyword means that the object referenced by the lvalue *nptr will be accessed only with it or a value directly derived from it.

However, a lot of programmers, and even experienced ones, use strtol in the following way:

#include <stdlib.h>

strtol (p, &p, 10);

In that case, **endptr == **&p == *p == *nptr, and the behavior is undefined. Is it right?

Solution

  • No. Nothing is accessed via **endptr in strtol. Only *endptr, a completely separate object, is accessed.