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C Style Strings

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
Jun 1 '06 #1
89 5191

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

Jun 1 '06 #2
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
Jun 1 '06 #3
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
Jun 1 '06 #4
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

Jun 1 '06 #5
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

Jun 1 '06 #6
"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
Jun 1 '06 #7
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)
Jun 1 '06 #8
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

Jun 1 '06 #9
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

Jun 1 '06 #10

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