Problem with strcmp()....

This is a discussion on Problem with strcmp().... within the C Programming forums, part of the General Programming Boards category; Code: #include <stdio.h> #include <getopt.h> #include <string.h> void ProcedeWithProg(int pwdYESNO) { char * string; char prompt[100]=""; char * hostNamePtr = ...

  1. #1
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    Sep 2005
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    Problem with strcmp()....

    Code:
    #include <stdio.h>
    #include <getopt.h>
    #include <string.h>
    
    void ProcedeWithProg(int pwdYESNO)
    {
       char * string;
       char prompt[100]="";
       char * hostNamePtr = getenv("HOSTNAME");
       char * pwdPtr = getenv("PWD");
       char * colon = ":";
       char exitstring[] = "exit";
       int bytes_read;
       int nbytes = 100;
      
       
       if(!pwdYESNO)
       {
          strcpy(prompt, hostNamePtr);
       }
       else
       {
          strcpy(prompt, hostNamePtr);
          strcat(prompt, colon);
          strcat(prompt, pwdPtr);
       } 
    
       /*Problem is here*/
       do
       {
          printf("%s:> ", prompt);
          string = malloc (nbytes + 1);
          bytes_read = getline (&string, &nbytes, stdin);
       
          if (bytes_read == -1)
          {
             printf("ERROR!\n", prompt);
          }
          else
          {
             printf("You Typed: %s", string);
          }
               
       } while (strcmp(exitstring, string) != 0);
    }
    The loop never ends because strcmp never spits out a 0. My best guess is that it's doing this because string is a pointer. Is this correct? The thing is I can''t get the getline function to work without string being a pointer. Is there a way I could either: Get strcmp to work with string being a pointer, or get getline to work with string not being a pointer? Thanks

  2. #2
    and the hat of wrongness Salem's Avatar
    Join Date
    Aug 2001
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    It's because the line returned has a newline and that's what always causes the mis-match

    Try strncmp(exitstring, string,4) != 0

    > string = malloc (nbytes + 1);
    You don't free it, this is a memory leak.
    malloc it once outside your do while loop, and free it when the loop exits.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  3. #3
    Gawking at stupidity
    Join Date
    Jul 2004
    Location
    Oregon, USA
    Posts
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    All strings are pointers. Your problem is you didn't read the first paragraph of getline()'s man page

    DESCRIPTION
    getline() reads an entire line, storing the address of the
    buffer containing the text into *lineptr. The buffer is
    null-terminated and includes the newline character, if a
    newline delimiter was found.
    So when you type "exit" the buffer contains "exit\n". strcmp("exit", "exit\n") will never be 0.

    EDIT: Aww, Salem beat me to it.
    Last edited by itsme86; 09-02-2005 at 12:30 PM.
    If you understand what you're doing, you're not learning anything.

  4. #4
    Registered User
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    Sep 2005
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    41
    thanks guys

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