regarding "initializer element is not constant"

MK27 · 08-23-2008, 06:23 PM

why do i get this error
test.c:6: warning: initializer element is not constant
test.c:6: warning: (near initialization for ‘len’)

when i compile this with "len" as a global int (as shown). It doesn't happen if "len" is localized within main().

Code:

  1 #include <string.h>
  2 #include <stdio.h>
  3 
  4 #define this "that"
  5 
  6 int len = strlen(this);
  7 int main () {
  8         printf("%d\n", len);
  9 }

iMalc · 08-23-2008, 07:04 PM

strlen is evaluated at runtime, not compile-time, as such it must be inside a function.
Note that some compilers might be able to optimise it to a compile-time constant, but that doesn't make it valid to assume that you're allowed to do what you're trying to do.

MK27 · 08-23-2008, 07:14 PM

well i guess that makes sense, since there really is no reason to apply strlen to a global constant anyway -- except sometimes I am lazy about counting...

King Mir · 08-23-2008, 10:35 PM

You can use sizeof() to get the length of a literal string.

zacs7 · 08-23-2008, 11:30 PM

Just be careful,

1. You can't use it on pointers to literals
2. It includes the NUL terminator, ie strlen(x) == sizeof(x) - 1

Not that 1 matters in this case

Code:

[zac@neux sandbox]$ gcc -W -Wall -std=c99 -pedantic -O0 sandbox.c -o sandbox
[zac@neux sandbox]$ cat sandbox.c
#include <stdio.h>

#define test "four"

const int len = sizeof(test);

int main(void)
{
    printf("%s = %d\n", test, len);
    return 0;
}
[zac@neux sandbox]$ ./sandbox 
four = 5

08-23-2008, 06:23 PM	#1
MK27 subminimalist Join Date: Jul 2008 Location: NYC Posts: 3,946	regarding "initializer element is not constant" why do i get this error test.c:6: warning: initializer element is not constant test.c:6: warning: (near initialization for ‘len’) when i compile this with "len" as a global int (as shown). It doesn't happen if "len" is localized within main(). Code: 1 #include <string.h> 2 #include <stdio.h> 3 4 #define this "that" 5 6 int len = strlen(this); 7 int main () { 8 printf("%d\n", len); 9 } __________________ Accuracy and integrity mean nothing if you don't make it past the censors...PYTHAGORAS
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08-23-2008, 07:04 PM	#2
iMalc Algorithm Dissector Join Date: Dec 2005 Location: New Zealand Posts: 2,476	strlen is evaluated at runtime, not compile-time, as such it must be inside a function. Note that some compilers might be able to optimise it to a compile-time constant, but that doesn't make it valid to assume that you're allowed to do what you're trying to do. __________________ My homepage Advice: Take only as directed - If symptoms persist, please see your debugger
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08-23-2008, 07:14 PM	#3
MK27 subminimalist Join Date: Jul 2008 Location: NYC Posts: 3,946	well i guess that makes sense, since there really is no reason to apply strlen to a global constant anyway -- except sometimes I am lazy about counting... __________________ Accuracy and integrity mean nothing if you don't make it past the censors...PYTHAGORAS
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08-23-2008, 10:35 PM	#4
King Mir Registered User Join Date: Apr 2006 Posts: 1,193	You can use sizeof() to get the length of a literal string. __________________ It is too clear and so it is hard to see. A dunce once searched for fire with a lighted lantern. Had he known what fire was, He could have cooked his rice much sooner.
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08-23-2008, 11:30 PM	#5
zacs7 Woof, woof! Join Date: Mar 2007 Location: Australia Posts: 3,139	Just be careful, 1. You can't use it on pointers to literals 2. It includes the NUL terminator, ie strlen(x) == sizeof(x) - 1 Not that 1 matters in this case Code: [zac@neux sandbox]$ gcc -W -Wall -std=c99 -pedantic -O0 sandbox.c -o sandbox [zac@neux sandbox]$ cat sandbox.c #include <stdio.h> #define test "four" const int len = sizeof(test); int main(void) { printf("%s = %d\n", test, len); return 0; } [zac@neux sandbox]$ ./sandbox four = 5 __________________ "I.T. gets the chicky-babes" - M. Kelly bakefile \| vim
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