From: merkur AT my-deja DOT com
Newsgroups: comp.os.msdos.djgpp
Subject: Re: sprintf woes
Date: Tue, 15 Feb 2000 21:37:21 GMT
Organization: Deja.com - Before you buy.
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References: <87pssv$12f$1 AT nnrp1 DOT deja DOT com>
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To: djgpp AT delorie DOT com
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In article <87pssv$12f$1 AT nnrp1 DOT deja DOT com>,
  mrdang AT my-deja DOT com wrote:
> I am having a lot of trouble with sprintf.  I
can not seem to make it
> do what I want within a subroutine /
procedure.  As an example:
>
> #include <stdio.h>
>
> void testing(void);
>
> int main()
> {
> 	char *f, *g, *j;
>
> 	testing();
> 	testing();
>
> 	sprintf(f, "q");
> 	sprintf(g, "w");
>
> 	printf("%s\n", f);
> 	printf("%s\n", g);
>
> 	sprintf(j, "s: %s %s", f, g);
> 	printf("%s\n\n", j);
>
> 	return 0;
> }
>
> void testing()
> {
> 	char *t, *m, *h;
>
> 	sprintf(m, "b");
> 	sprintf(h, "d");
>
> 	printf("%s\n", m);
> 	printf("%s\n", h);
>
> 	sprintf(t, "s: %s %s", m, h);
> 	printf("%s\n\n", t);
> }
>
> The above gives me:
> (null)
> (null)
> (null)
>
> (null)
> (null)
> (null)
>
> q
> w
> s: q w
>
> When I wanted it to give me:
> b
> d
> s: b d
>
> b
> d
> s: b d
>
> q
> w
> s: q w
>
> Can anybody point out whjat I am doing wrong
here?  Thanks :)
>
> Dan G
>
> Sent via Deja.com http://www.deja.com/
> Before you buy.
>
Hello Dan

In the above code all the pointers (f. g, j etc)
are not initialized i.e. they point to an unknown
memory location. Writing to these pointers can
crash your system.
If you want to format strings with sprintf you
need to allocate a char buffer

char   buffer[20];
char   *pc = &buffer[0];  // Initialize pointer

Then you can use sprintf to generate a formatted
string

sprintf (pc, "Hello");

Printing the string with

printf ("String: %s\n", pc);

should produce the output

String: Hello

If your buffer is 20 bytes in length you can only
write 19 bytes of text because 1 byte is needed
for the terminating \0 (eos) character.

MR





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Before you buy.