Thread: Simple String Manipulation (Beginner question)

  1. #1
    Registered User
    Join Date
    Feb 2009

    Simple String Manipulation (Beginner question)

    I've just started learning C and am having some trouble.

    Lets say you have these two strings.

    char a [5] = "abcd";
    char b [3] = "zz";

    I want to use strcpy() and strcat() to change b into "bd".

    Something like,

    strcpy(b, a[1]);
    strcat(b, a[3]);

    Clearly, this does not work.
    a[1] is not a string. I have no idea how to get a "b" string from the variable a.

    Any help?

  2. #2
    Registered User
    Join Date
    Nov 2008
    If the string is actually that short you can manipulate it as a character array.

    strcpy(string,string[location]) wont work b/c you are using a function to copy one string into another to copy one character into a string. If you want to copy one char to a string you should try
    strcpy(string,"c"). I think anything b/w quotes can be considered a string literal. You should google strcpy.

  3. #3
    Registered User
    Join Date
    Dec 2008
    Black River
    In order to get "b" from the string a, you would have to do &a[1]. However, because both strcpy and strcat expect null terminated strings, you can't really use them in your example. On the other hand, you could use something like strncpy and strncat to achieve what you want:

    char a[] = "abcd";
    char b[] = "zz";
    strncpy(b, &a[1], 1);
    strncat(b, &a[3], 1);
    However, for simple cases like what you've got, you're MUCH better using direct assignment (IE: using strcpy or memcpy with "bd" as the concatenating argument)

  4. #4
    spurious conceit MK27's Avatar
    Join Date
    Jul 2008
    segmentation fault
    Also this can happen:
    's'ingle quotes
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

  5. #5
    Kernel hacker
    Join Date
    Jul 2007
    Farncombe, Surrey, England
    Or, if you really want to do what is in the original post, as closely as possible, with the least overhead:
    b[0] = a[1];
    b[1] = a[3];
    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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