replace function

[Hilary Cotter]

I'm trying to replace the characters in a pointer from an url string.

Here is my code.

// string has embedded '+', this code will not work.
VOID PatchQuery(char *szQuery, char **ppszPatchedQu ery)
{
char *p = szQuery;

while (*p++)
{
if (*p == '+') //replace '+' by ' '
*p = ' ';

}
strcpy(begin,p) ;
*ppszPatchedQue ry =begin;
return;
}

I get an access violation when I try to replace the + with a space.
Can anyone tell me how to do this?

TIA

[Ema]

Re: replace function

"Hilary Cotter" <hilaryk@att.ne t> ha scritto nel messaggio
news:3bccc79e.0 309030415.55bcb d79@posting.goo gle.com...[color=blue]
> I'm trying to replace the characters in a pointer from an url string.
>
> Here is my code.
>
> // string has embedded '+', this code will not work.
> VOID PatchQuery(char *szQuery, char **ppszPatchedQu ery)
> {
> char *p = szQuery;
>
> while (*p++)
> {
> if (*p == '+') //replace '+' by ' '
> *p = ' ';
>
> }
> strcpy(begin,p) ;
> *ppszPatchedQue ry =begin;
> return;
> }
>
> I get an access violation when I try to replace the + with a space.
> Can anyone tell me how to do this?
>[/color]


where is declared "begin"?

Bye,
Ema

[Nick Austin]

Re: replace function

On 3 Sep 2003 05:15:11 -0700, hilaryk@att.net (Hilary Cotter) wrote:
[color=blue]
>I'm trying to replace the characters in a pointer from an url string.
>
>Here is my code.
>
>// string has embedded '+', this code will not work.
>VOID PatchQuery(char *szQuery, char **ppszPatchedQu ery)
>{
> char *p = szQuery;
>
> while (*p++)
> {
> if (*p == '+') //replace '+' by ' '
> *p = ' ';
>
> }
> strcpy(begin,p) ;[/color]

p is no longer pointing at a valid object, ITYW:

strcpy(begin,sz Query);
[color=blue]
> *ppszPatchedQue ry =begin;
> return;
>}[/color]

Also why modify the original string then make a copy of it? It
would be more logical to swap the order so that the original is
not destroyed.
[color=blue]
>I get an access violation when I try to replace the + with a space.
>Can anyone tell me how to do this?[/color]

Nick.

[Pieter Droogendijk]

Re: replace function

On 3 Sep 2003 05:15:11 -0700
hilaryk@att.net (Hilary Cotter) wrote:[color=blue]
> I'm trying to replace the characters in a pointer from an url string.
>
> Here is my code.
>
> // string has embedded '+', this code will not work.[/color]

Invalid syntax in C89 (hint: C++ style comments)
[color=blue]
> VOID PatchQuery(char *szQuery, char **ppszPatchedQu ery)[/color]

What's VOID?
[color=blue]
> {
> char *p = szQuery;
>
> while (*p++)
> {
> if (*p == '+') //replace '+' by ' '
> *p = ' ';[/color]

might attempt to overwrite read-only strings!
[color=blue]
>
> }
> strcpy(begin,p) ;
> *ppszPatchedQue ry =begin;[/color]

You make a copy too late... copy the string BEFORE modifying it.
And what's 'begin'?
[color=blue]
> return;
> }
>
> I get an access violation when I try to replace the + with a space.
> Can anyone tell me how to do this?[/color]

You're probably trying to write to something you're not supposed to write to
(read-only string or string literal). Are you calling it like this:

PatchQuery ("stringwith +es and +es", foo);

If so, you're trying to overwrite a string literal, which is not allowed.
This may be a better function for you:

#include <string.h>
int patchquery (char *string, char **retstring)
{
char *sptr;
/* make a copy of the original string and modify it instead of the original */
*retstring = sptr = strdup (string);
if (!sptr)
return 0;
for (;*sptr;sptr++)
if (*sptr == '+')
*sptr = ' ';
/* retstring already holds the pointer to our (modified) copy */
return 1;
}

Do remember to free() the string returned in retstring.

--
char*x(c,k,s)ch ar*k,*s;{if(!k) return*s-36?x(0,0,s+1):s ;if(s)if(*s)c=1 0+(c?(x(
c,k,0),x(c,k+=* s-c,s+1),*k):(x(* s,k,s+1),0));el se c=10;printf(&x( ~0,0,k)[c-~-
c+"1"[~c<-c]],c);}main(){x(0 ,"^[kXc6]dn_eaoh$%c","-34*1'.+(,03#;+, )/'///*");}

[Ivan Vecerina]

Re: replace function

Hi,

"Hilary Cotter" <hilaryk@att.ne t> wrote in message
news:3bccc79e.0 309030415.55bcb d79@posting.goo gle.com...
| // string has embedded '+', this code will not work.
| VOID PatchQuery(char *szQuery, char **ppszPatchedQu ery)

As Ema pointed out, the code you posed does not compile...
But from the function's signature and code snippet, I see
two things that can go wrong:

- The type of the char **ppszPatchedQu ery suggests that
the PatchQuery function will use it to return a pointer
to a newly allocated memory buffer. Is this intended ?
This is not what the function currently does...
Suggestion: consider letting the caller allocate
the destination buffer...

- If your function is called by passing a string literal
as the first parameter, the function may trigger an
access violation, as it modifies the contents
of szQuery.
PatchQuery("a+b ",&pbuf); // will crash
Suggestion: do not modify the source string. Only
modify the copy you create.

| I get an access violation when I try to replace the + with a space.
| Can anyone tell me how to do this?

I'm afraid this could be homework... but here's a way
to implement equivalent functionality:
void patch_query(cha r const* src, char* dst)
{
char c;
do {
c = *src++;
*dst++ = (c=='+') ? ' ' : c;
} while(c);
}


Cheers,
--

http://www.post1.com/~ivec

[Eric Sosman]

Re: replace function

Hilary Cotter wrote:[color=blue]
>
> I'm trying to replace the characters in a pointer from an url string.
>
> Here is my code.
>
> // string has embedded '+', this code will not work.
> VOID PatchQuery(char *szQuery, char **ppszPatchedQu ery)
> {
> char *p = szQuery;
>
> while (*p++)
> {
> if (*p == '+') //replace '+' by ' '
> *p = ' ';
>
> }
> strcpy(begin,p) ;
> *ppszPatchedQue ry =begin;
> return;
> }[/color]

Others have diagnosed various problems here, but one I
haven't seen mentioned yet is the fact that a '+' at the
very beginning of the string will not be replaced: you're
incrementing `p' too early.

--
Eric.Sosman@sun .com