An interesting question about strcat

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  1. #1
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    An interesting question about strcat

    Why the following code prints "Huh?" ?
    It seems that 0xFF is never appended to the list by strcat?

    Code:
    #include <stdio.h>
    #include <string.h>
    
    const char * const eof = "\0xFF";
    char list[2000] = {0};
    
    void append (const char * flower)
    {
        strcat (list, flower);
        strcat (list, eof);
    }
    int main()
    {
        const char *next;
        append("Calla Lily");
        append("Daisy");
        append("Tulip");
        next = strchr(list, 0xFF);
        if (!next) printf ("Huh?\n");
    }

  2. #2
    C++ Witch laserlight's Avatar
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    Change this:
    Code:
    const char * const eof = "\0xFF";
    to:
    Code:
    const char * const eof = "\xFF";
    The former embeds a null character followed by "FF", thus nothing was concatenated.

    By the way, if this was supposed to be specifically C rather than the C part of C++, say the word and I shall move the thread. Otherwise, you should #include <cstdio> and <cstring> instead.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  3. #3
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    Thanks lot.
    1) Why strchr needs 0xFF with 0 at the beginning? Why not eof = "\0xFF"?
    2) Why strchr does not need to escape 0 ?

  4. #4
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by meili100
    1) Why strchr needs 0xFF with 0 at the beginning? Why not eof = "\0xFF"?
    0xFF is an int. "\0xFF" is a string. If you want to use a character constant, then it should be '\xFF'.

    Quote Originally Posted by meili100
    2) Why strchr does not need to escape 0 ?
    It is not about strchr, but the fact that the literal is an int literal.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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