String literals

String literals

[zeljko oluic]

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Hi dear fellow,
 
I am having a problem running the enclosed test program. I expected
program to pass the test points 1, 2 and 3 but instead it cored at point
2 (3). After looking into generated assembler code I noticed that
string literals casted to array initializers (see pointers S2
and s3) were put into read only segment. Is this correct (i.e. in compilance
with ANSI C standard ) ?
I am running gcc version 2.95.2 19991024 on SCO UNIX.
 
 
Thanks for your help,
 
Zeljko Oluic
 
Enc. strings test program
 
#include <stdio.h>
 
 
char S1[] = "can be modified";
char *S2 = (char []) {"can be modified too"};
 
 
void
string_constant(void)
{
    char *s1;
    char *s2;
    char *s3;
 
 
    s1 = "if modified possible run-time error";
    s2 = "if modified possible run-time error";
    s3 = (char []) {"can be modified too"};
 
 
    if (s1 == s2) printf("shared strings\n");
    else printf("strings are not shared\n");
 
    printf("the following need to be ok\n");
    printf("1\n");
    S1[0] = 'x';
    printf("2\n");
    S2[0] = 'x';
    printf("3\n");
    s3[0] = 'x';
 
    printf("the following can cause a run-time error\n");
    s1[0] = 'x';
 
    if (*s1 == 'x')  printf("strings are writable\n");
    else printf("strings are not writable\n");
}

Re: String literals

[Martin v. Loewis]

> I am having a problem running the enclosed test program. I expected
> program to pass the test points 1, 2 and 3 but instead it cored at
> point 2 (3). After looking into generated assembler code I noticed
> that string literals casted to array initializers (see pointers S2
> and s3) were put into read only segment. Is this correct (i.e. in
> compilance with ANSI C standard ) ?

Yes, this is indeed in compliance with the ISO C standard. gcc has an
option -fwritable-strings if you really need that function.

Regards,
Martin