concatenate int onto char

This is a discussion on concatenate int onto char within the C Programming forums, part of the General Programming Boards category; How can I convert an integer to a string for inclusion in another string? eg, here's a try with typecasting ...

  1. #1
    spurious conceit MK27's Avatar
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    concatenate int onto char

    How can I convert an integer to a string for inclusion in another string? eg, here's a try with typecasting that doesn't work:
    Code:
    int main () {
            int x=5;
            char *str=(char*)x;
            printf("%s", str);
    }
    Compiles fine but segfaults.
    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

  2. #2
    Kernel hacker
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    Yes, it would crash. You are trying to read a string from locaiton 5 in memory.

    To concatenate a number to a string, you need to convert the internal (binary) representation to a string, and then concatenate the string. An easy way to do that would be to use sprintf() to "print" the number into a string buffer - you could even do something like this:
    Code:
       char buffer[100];
       int n = 12;
       ...
       sprintf(buffer, "Test%03d.txt", n);
       ...
    Buffer would in this case contain a string "Test012.txt"

    --
    mats
    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.

  3. #3
    Registered User slingerland3g's Avatar
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    You may want to thank about the following:

    Code:
    #include <stdlib.h>
    
    /*Prototype */
    char *itoa(int value, char *string, int radix);

  4. #4
    and the hat of sweating
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    Code:
    itoa( num, strOut, 10 );
    which is compiler specific, or
    Code:
    sprintf( strOut, "%d", num );
    which is standard C.

  5. #5
    spurious conceit MK27's Avatar
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    ahh, now that was nice and simple (sprintf)...thanx
    Last edited by MK27; 08-06-2008 at 10:59 AM.
    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

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