haven't used C/C++ in a while....so this might be really simple for most of you....

can someone please tell me how to concatenate two char * strings?
(one of them is const char* and the other one isn't)

eg.
char * c1 = "SYSTEM PATH = ";
char *c2 = getenv("PATH");

how do I concatenate c1 + c2 and put the result into a third char * variable?

I've tried strcat() but since c2 points to a string without the explicit '\0' character, the program crashes.

thanks very much.

-sameer

Code:

#include <iostream>
#include <cstdlib>
#include <string>

int main()
{
   std::string a = "SYSTEM PATH = ";
   char *b = getenv("PATH");
   if ( b )
   {
      a += b;
   }
   std::cout << a << std::endl;
   return 0;
}

Originally Posted by Dave_Sinkula

Code:

#include <iostream>
#include <cstdlib>
#include <string>

int main()
{
   std::string a = "SYSTEM PATH = ";
   char *b = getenv("PATH");
   if ( b )
   {
      a += b;
   }
   std::cout << a << std::endl;
   return 0;
}

^those aren't two char* variables... but he does have a good point - since you're using C++, you can take advantage of the string class.

AFAIK, there is no way to do that with char* variables unless you know the length of the first one...

Are you sure the return value of of getenv, which in this case is c2, isn't null terminated? I think it is. You need to allocate space for the combined string. Since neither of the buffers, c1 or c2, should be modified, you need to create a third buffer, allocate enough space for both strings and a null terminator, strcpy the first string into the result buffer, and then strcat the second string on to the end.

I agree with Daved. getenv returns a null-terminated string. If it didn't, the concatenation operator of the std::string class would not work correctly either. Consider this example:

Code:

int main()
{
   std::string a = "SYSTEM PATH = ";
   char *b = getenv("PATH");
   if ( b )
   {
      a += b;
   }
   std::cout << a << std::endl;

   a = "SYSTEM PATH = ";   //reset a
   char c[10] = "123456789";   //create a string
   c[9] = '0';   //remove null termination
   a += c;   //concatenate
   std::cout << a << std::endl;
   return 0;
}

What's worse, if it wasn't NUL-terminated, there would be absolutely no way to find out the length. There is no getenvlen function.