C Style Strings

[scroopy]

Hi,

I've always used std::string but I'm having to use a 3rd party library
that returns const char*s. Given:

char* pString1 = "Blah ";
const char* pString2 = "Blah Blah";

How do I append the contents of pString2 to pString? (giving "Blah
Blah Blah")

I looked at strcat but that crashes with an unhandled exception.

Thanks

[jpalecek]

scroopy wrote:

Hi,

I've always used std::string but I'm having to use a 3rd party library
that returns const char*s. Given:

char* pString1 = "Blah ";
const char* pString2 = "Blah Blah";

How do I append the contents of pString2 to pString? (giving "Blah
Blah Blah")

I looked at strcat but that crashes with an unhandled exception.

That's easy, do it the C way:

char* result=new char[strlen(s1)+strl en(s2)+1];
strcpy(result,s 1);
strcat(result,s 2);

Regards
Jiri Palecek

[Kai-Uwe Bux]

scroopy wrote:

Hi,

I've always used std::string but I'm having to use a 3rd party library
that returns const char*s. Given:

char* pString1 = "Blah ";
const char* pString2 = "Blah Blah";

How do I append the contents of pString2 to pString? (giving "Blah
Blah Blah")

a) Keep using std::string for your own stuff. The std::string class has
methods that allow you to interact with C-style string interfaces of
libraries.

b) Note that in your example above, pString1 is initialized to a const
string. Any attempt to modify that string would be undefined behavior. The
danger lies in not declaring pString1 as a char const *.

c) You could do:

#include <string>
#include <algorithm>

char * strdup ( std::string str ) {
char * result = new char [ str.length() +1 ];
std::copy( str.begin(), str.end(), result );
result[ str.length() ] = 0;
return ( result );
}

int main ( void ) {
char * pString1 = "Blah ";
char const * pString2 = "Blah Blah";
pString1 = strdup( std::string( pString1 ).append( pString2 ) );
}
However, I would prefer to use std::string for my own stuff:

#include <string>

int main ( void ) {
std::string pString1 = "Blah "; // rhs returned by some library
std::string pString2 = "Blah Blah"; // rhs returned by some library
pString1.append ( pString2 );
}
Best

Kai-Uwe Bux

[Roland Pibinger]

On Thu, 01 Jun 2006 08:35:36 +0100, scroopy <sc*****@nospam .com>
wrote:

I've always used std::string but I'm having to use a 3rd party library
that returns const char*s.
First you need to find out if you 'own' the returned string, i.e. if
you must free (maybe delete) the returned char*. Good C libraries
usually don't require the user to call free.
Given:

char* pString1 = "Blah ";
const char* pString2 = "Blah Blah";

How do I append the contents of pString2 to pString? (giving "Blah
Blah Blah")

You can append a const char* to a std::string:

string myString = "Blah ";
const char* s = myLibFunc (...);
if (s) {
myString += s; // or myString.append (s);
}
// free (s); // if it's a bad lib

Best wishes,
Roland Pibinger

[kwikius]

scroopy wrote:

Hi,

I've always used std::string but I'm having to use a 3rd party library
that returns const char*s. Given:

char* pString1 = "Blah ";
const char* pString2 = "Blah Blah";

How do I append the contents of pString2 to pString? (giving "Blah
Blah Blah")

#include <malloc.h>
#include <cstring>

char* concat(const char * str1, const char* str2)
{
char * result = (char*) malloc(strlen( str1) + strlen (str2) + 1);
if( result != NULL){
strcpy(result,s tr1);
strcat(result, str2);
}
return result;
}

#include <iostream>
#include <string>

char* pString1 = "Blah ";
const char* pString2 = "Blah Blah";
int main()
{
// C-style
char* str = concat(pString1 ,pString2);
if(str != NULL){
std::cout << str <<'\n';
free(str);
}

// C++ style
std::string str1=std::strin g(pString1) + pString2;
std::cout << str1 <<'\n';
}

I'm not sure if that is the optimal C method. Its interesting to note
how much better the C++ version is though!

regards
Andy Little

[kwikius]

Roland Pibinger wrote:

First you need to find out if you 'own' the returned string, i.e. if
you must free (maybe delete) the returned char*. Good C libraries
usually don't require the user to call free.

Out of interest ... What is a good C library resource management
strategy? ... for example (say) modifying the following example

char* concat(const char * str1, const char* str2)
{
char * result = (char*) malloc(strlen( str1) + strlen (str2) + 1);
if( result != NULL){
strcpy(result,s tr1);
strcat(result, str2);
}
return result;
}

char* pString1 = "Blah ";
const char* pString2 = "Blah Blah";

int main()
{
char* str = concat(pString1 ,pString2);
if(str != NULL){
std::cout << str <<'\n';
free(str); // How to avoid this in C-style?
}
}

regards
Andy Little

[Richard Bos]

"kwikius" <an**@servocomm .freeserve.co.u k> wrote:

scroopy wrote:

How do I append the contents of pString2 to pString? (giving "Blah
Blah Blah")
#include <malloc.h>
#include <cstring>

This is not C...
char* concat(const char * str1, const char* str2)
{
char * result = (char*) malloc(strlen( str1) + strlen (str2) + 1);

....and this is the wrong way to do this in C. And, really, also in C++:
use new.

So don't cross-post stuff like that. Follow-ups set.

Richard

[Richard Heathfield]

Richard Bos said:

"kwikius" <an**@servocomm .freeserve.co.u k> wrote:

scroopy wrote:

> How do I append the contents of pString2 to pString? (giving "Blah
> Blah Blah")

#include <malloc.h>
#include <cstring>

This is not C...

....and it's not C++ either, so I'm not sure why you set followups to clc++.

The entire article, in fact (his, not yours), was a classic example of the
kind of thing you get in the Hackitt and Scarper school of programming.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)

[kwikius]

Richard Bos wrote:

"kwikius" <an**@servocomm .freeserve.co.u k> wrote:

scroopy wrote:

How do I append the contents of pString2 to pString? (giving "Blah
Blah Blah")
#include <malloc.h>
#include <cstring>

This is not C...

char* concat(const char * str1, const char* str2)
{
char * result = (char*) malloc(strlen( str1) + strlen (str2) + 1);

...and this is the wrong way to do this in C.

Out of interest what is the right way? BTW... It would seem to me to
make sense to cross-post this to comp.lang.c as it is somewhat O.T. for
C++. I think It makes sense in terms of a language comparison though,
don't you think?
And, really, also in C++:
hmmm... Touchy arent we? I showed a C++ way in my previous post.
use new.
Sure? .. The best way is not to allocate resources the users has to
manage , isnt it?.
So don't cross-post stuff like that. Follow-ups set.

Hmm... Are you sure I wouldnt get a better answer to the how to do it
in C question in a C newsgroup?

regards
Andy Little

[kwikius]

Richard Heathfield wrote:

Richard Bos said:

"kwikius" wrote:

scroopy wrote:
> How do I append the contents of pString2 to pString? (giving "Blah
> Blah Blah")

#include <malloc.h>
#include <cstring>

This is not C...

...and it's not C++ either, so I'm not sure why you set followups to clc++.

The entire article, in fact (his, not yours), was a classic example of the
kind of thing you get in the Hackitt and Scarper school of programming.

Thats great! Thanks! Its always good to get positive feedback!

regards
Andy Little