C string append

Question

I want to append two strings. I used the following command:

new_str = strcat(str1, str2);

This command changes the value of str1

Answer 1

man page of strcat says that arg1 and arg2 are appended to arg1.. and returns the pointer of s1. If you dont want disturb str1,str2 then you have write your own function.

char * my_strcat(const char * str1, const char * str2)
{
   char * ret = malloc(strlen(str1)+strlen(str2));

   if(ret!=NULL)
   {
     sprintf(ret, "%s%s", str1, str2);
     return ret;
   }
   return NULL;    
}

Hope this solves your purpose

Answer 2

You'll have to strncpy str1 into new_string first then.

Answer 3

I needed to append substrings to create an ssh command, I solved with sprintf (Visual Studio 2013)

char gStrSshCommand[SSH_COMMAND_MAX_LEN]; // declare ssh command string

strcpy(gStrSshCommand, ""); // empty string

void appendSshCommand(const char *substring) // append substring
{
  sprintf(gStrSshCommand, "%s %s", gStrSshCommand, substring);
}

Answer 4

do the following:

strcat(new_str,str1);
strcat(new_str,str2);