Do I misunderstand this example about scope of string literals?

Question

I was reading up on common C pitfalls and came up to this article on some famous Uni website. (It is the 2nd link that comes up on google).

The last example on that page is,

// Memory allocation on the stack
void b(char **p) {
    char * str="print this string";
    *p = str;
}

int main(void) {
    char * s;
    b(&s);
    s[0]='j'; //crash, since the memory for str is allocated on the stack, 
              //and the call to b has already returned, the memory pointed to by str 
              //is no longer valid.
    return 0;
}

That explanation in the comment got me thinking then, that, isn't the memory for string literals not static?

Isn't the actual error there then that you are not supposed to modify string literals, because it is undefined behavior? Or are the comments there correct and my understanding of that example is wrong?

Upon searching further, I saw this question: referencing a char that went out of scope and I understood from that question that, the following is valid code.

#include <malloc.h>
char* a = NULL;
{
    char* b = "stackoverflow";
    a = b;
}

int main() {
    puts(a);
}

Also this question agrees with the other stackoverflow question and my thinking, but opposes the comment from that website's code.

To test it, I tried the following,

#include <stdio.h>
#include <malloc.h>

void b(char **p)
{
    char * str = "print this string";
    *p = str;
}

int main(void)
{
    char * s;
    b(&s);
    // s[0]='j'; //crash, since the memory for str is allocated on the stack,
                //and the call to b has already returned, the memory pointed to by str is no longer valid.
    printf("%s \n", s);
    return 0;
}

which as expected does not give a segmentation fault.

Answer 1

Standard says (emphasize is mine):

6.4.5 String literals

6. [...] The multibyte character sequence is then used to initialize an array of static storage duration and length just sufficient to contain the sequence. [...]

7. [...] If the program attempts to modify such an array, the behavior is undefined. [...]