Thread: delete new char[] correctly ?

  1. #1
    Registered User
    Join Date
    Jan 2020

    delete new char[] correctly ?

    Hi padawan here So do l have this situacion. l call a function twice that returns a c-string, and l save into the same char* pointer (* c_string). but is correct to delete that (* c_string) before assigning the return value again to foo() ?. Because if l dont part of the content remains, when l stepped in the debugger l can see it. Thanks in advance.

    char *foo (const char *_s) {
       char *str = new char[40];
       strcpy(str, _s);
       strcat(str, " *** ");
       strcat(str, _s);
       return str;
    int main(int argc, char* argv[]) {
       char *c_string;
       c_string = foo("monster");
       printf("%s\n", c_string);
       delete []c_string; // is this correct before calling foo() again?
       c_string = foo("paragraph another");
       printf("%s\n", c_string);
       delete []c_string;
       return 0;

  2. #2
    C++ Witch laserlight's Avatar
    Join Date
    Oct 2003
    Yes, you should do so otherwise you technically have a memory leak (although this is a short running program so it doesn't matter).
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  3. #3
    Registered User
    Join Date
    Jan 2020
    thats what l was thinking thank you. Yes this a small part of a program.

  4. #4
    Registered User
    Join Date
    Feb 2019
    Another tip, using only ISO functions from string.h:

    char *foo( char *s )
      char *p;
      char tmp;
      ssize_t size;
      // get the size of final string.
      size = snprintf( &tmp, 1, "%s *** %s", s, s );
      // allocate space, fill the buffer and return the pointer.
      p = new char[size+1];
      sprintf( p, "%s *** %s", s, s );
      return p;

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