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Problem with array of strings !!

This is a discussion on Problem with array of strings !! within the C Programming forums, part of the General Programming Boards category; Hi, Please excuse me for asking such a trivial question. I am very new to C programming and it would ...

  1. #1
    Registered User
    Join Date
    Sep 2012
    Posts
    6

    Problem with array of strings !!

    Hi,

    Please excuse me for asking such a trivial question. I am very new to C programming and it would be very helpful if someone answers my question.

    Here is my program ...

    Code:
    #include"scanner.h"
    #include<stdio.h>
    #include"scanner.c"
    #include<stdlib.h>
    #include<string.h>
    
    #define MAX_TOKENS 10
    
    int main(int argc, char **argv){
        int datatype, counter;
        int index = 0;
        char *my_argv[MAX_TOKENS];
        while((datatype = yylex()) != 6)
        {    
            printf("\nData :%s",yytext);
            printf("\nData type :%d\n",datatype);
            my_argv[index++] = yytext;
        }
        printf("\n%s",my_argv[0]);
        printf("\n%s",my_argv[1]);
    }
    Here yytext is of type char*. I store it in my_argv[]. Consider yytex returns "abc" and then "def". I should be getting the output as

    abc
    def

    but instead I get

    abc def
    def

    Can anyone explain me this !!

    Thanks in advance.

  2. #2
    Registered User
    Join Date
    Jun 2005
    Posts
    6,636
    The offending line is
    Code:
        my_argv[index++] = yytext;
    which simply copies a pointer.

    Copying pointers does not copy what they point at.

    1) ensure there is a buffer to be copied to.
    2) copy the required string to that buffer.

    You have completed neither of those steps. A simple way to achieve the first is to make my_argv into a 2-dimensional array (aka an array of arrays), rather than an array of pointers. To copy a string (step 2) look up the function strcpy().

    Also, never .... repeat never .... #include a .c file from another .c file. Simply compile the files separately, and link the objects together.

    Also, the offending line has two side effects (sets a value to my_argv[index] and then increment index). Unless you know exactly what you are doing - and, by your question, you don't - always make each statement have exactly one side effect.
    Code:
        my_argv[index] = yytext;
        ++index;
    (note you still need to fix the first line with this adjustment).
    Last edited by grumpy; 09-04-2012 at 05:29 AM.
    rags_to_riches likes this.
    Right 98% of the time, and don't care about the other 3%.

    If I seem grumpy or unhelpful in reply to you, or tell you you need to demonstrate more effort before you can expect help, it is likely you deserve it. Suck it up, Sunshine, and read this, this, and this before posting again.

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