🚀 go-pugleaf

luckas@igd.fhg.de (Volker Luckas) writes:

>it was very astonishing for me to recognize that the following piece of
>source code is accepted by gcc 2.7.2 (Solaris 2.5) without giving a
>warning if gcc is called in the following way: 

I'm not sure why this should be "astonishing", actually.

>gcc test.c -o test

>#include <string.h>

>int main( )
>{
>  char* str = "0.12345678";
>  double val = 1.11111111;

>  sprintf( str, "%lf", val );

>  printf( "Result: %s\n", str );

>  return 0;
>}

>The generated binary crashes if started afterwards. Interestingly this
>does not happen if you compile the source with cc from the Solaris 2.5
>Compiler package or even with gcc 2.7.2 running under IRIX 5.3

>Compiling the source with -Wall gives you a warning about implicitely
>defined functions but no warning about the illegal sprintf( ) call.

There is nothing illegal about that sprintf() call -- just the
questionable use of "%lf", and you do get a warning about that
one with -Wall.  sprintf() takes as its first argument a char*,
you are supplying it with a char*, what's illegal about that?

What is, not illegal, but VERY questionable, is initializing a
char* to a literal character string; however, the ANSI C standard
deems that to be legal.  If the first line was something like:
	char * str = (char*)123456;
you wouldn't be particularly astonished to see the resulting
program crash in some cases and not in others, would you?  At
least, I wouldn't be.

>Is there any possibility to avoid this kind of behaviour ???

You can add the -Wwrite-strings flag to your compilation line
in order to make a literal character string evaluate to a
const char *, rather than to a char * as the ANSI C standard
mandates.  If you do that, you'll get a warning about const
being implicitly cast away in the "char* str = ..." line.


Alex
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