Thread: reverse a word

  1. #1
    Registered User
    Join Date
    Sep 2008
    Manchester, UK

    reverse a word

    hello all,

    please help me to understand the following code; it compile fine but the it gives the correct result only for a word of length =< 3. However if I comment out the statement printf("len = %d\n",len) it works fine for all inputs.

    # include <stdio.h>
    # include <string.h>
    char *ptr;
    int main(int args, char *argv[]){
     int len = strlen(argv[1]);
     //printf("len = %d\n",len);
     int j = len - 1, i;
     char ch[len];
             for( ptr=argv[1],i=0; i<len; i++,j--){         
                  ch[i]=*(ptr + j); 

  2. #2
    Kernel hacker
    Join Date
    Jul 2007
    Farncombe, Surrey, England
    You probably want ch[len+1] and and then put ch[i] = '\0' after the reversing loop.

    Of course, ch[len] is non-standard even for C99 compilers, so if you want to follow C standard coding, you'd have to either use a statically sized buffer [remember to check the length before copying], or call malloc to allocate a suitable size string space [don't forget the +1 for the terminating zero].

    printf("%s\n", ch);
    is probably a better solution, as you would get "interesting" results if the user inputs "d%" or some such [and the right combination of % in the input may even cause a crash]

    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

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