Discussion
What will be the output of the following C code?
#include <stdio.h>
#include <string.h>
int main()
{
char *str = "hello, world";
char str1[9];
strncpy(str1, str, 9);
printf("%s %d", str1, strlen(str1));
}
Answer: C
Correct answer: Undefined behaviour
strncpy copies at most n characters and adds a terminating null only if the source is shorter than n. Here the source has 12 characters and n is 9, so all nine bytes of str1 are filled with hello, wo and no null is written. Passing that to printf("%s") and strlen reads past the end of the array - undefined behaviour.
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