pointers and strlen

This is a discussion on pointers and strlen within the C Programming forums, part of the General Programming Boards category; Hello I have this code Code: int mystrlen(char *string) { int len; char *p = string; for(; string[0] != '

Thread: pointers and strlen

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  1. #1
    ~viaxd() viaxd's Avatar
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    pointers and strlen

    Hello
    I have this code
    Code:
    int mystrlen(char *string) {
            
            int len;
            char *p = string;
    
    	for(; string[0] != '\0'; string++)
                           ;
    len = p - &string[0];
    return len;
    }
    It works but i dont how. I mean string[0] != '\0' will be always true if the string is > 0 and it is. How can len be the lenght if p points to the begining of string? I suppose p points wherever string does, right?
    I was wondering how can i write this function without pointer p..

    Thanks

  2. #2
    Just Lurking Dave_Sinkula's Avatar
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    >I was wondering how can i write this function without pointer p.
    Code:
    int mystrlen(const char *s)
    {
       int len = 0;
       while ( *s++ != '\0' )
       {
          ++len;
       }
       return len;
    }
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  3. #3
    ATH0 quzah's Avatar
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    Or do this:
    Code:
    int mystrlen(const char *s)
    {
       int len = 0;
       while ( s[len++] != '\0' );
    
       return len-1; /*edit*/
    }
    Or just do that:
    Code:
    int mystrlen( const char *s )
    {
        return *s == '\0' ? 0 : 1 + mystrlen( s+1 );
    }
    Or do...

    Quzah.
    Last edited by quzah; 08-23-2003 at 05:47 PM.
    Hope is the first step on the road to disappointment.

  4. #4
    End Of Line Hammer's Avatar
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    quzah, your first version doesn't work properly

    Another "or do":
    Code:
    int mystrlen(const char *s)
    {
       const char *p = s;
       while (*p) p++;
       return p - s;
    }
    When all else fails, read the instructions.
    If you're posting code, use code tags: [code] /* insert code here */ [/code]

  5. #5
    ATH0 quzah's Avatar
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    Originally posted by Hammer
    quzah, your first version doesn't work properly

    Another "or do":
    Yeah but at least it fit the criteria.

    Oh, and technicly, to fit criteria, you could rename your pointer 'q' instead of 'p' and do it "without pointer p".

    Quzah.
    Hope is the first step on the road to disappointment.

  6. #6
    End Of Line Hammer's Avatar
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    >>but at least it fits the criteria
    Doh, I didn't even bother reading that
    When all else fails, read the instructions.
    If you're posting code, use code tags: [code] /* insert code here */ [/code]

  7. #7
    ATH0 quzah's Avatar
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    Here's another way:
    Code:
    int mystrlen( const char *s )
    {
        return strlen(s);
    }


    #define mystrlen strlen

    But now I'm just being ridicules.

    Quzah.
    Hope is the first step on the road to disappointment.

  8. #8
    Been here, done that.
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    Originally posted by quzah
    Here's another way:
    Code:
    int mystrlen( const char *s )
    {
        return strlen(s);
    }
    I knew someone would show this one -- I was afraid it was going to be me! Thanks for beating me to it, Q
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    poly meaning many and
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  9. #9
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    >len = p - &string[0];

    I was getting negative numbers using the above.
    len = &string[0] - p;

  10. #10
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    Hammer, your code should be:
    Code:
    int mystrlen(char *s)
    {
       const char *p = s;
       while(*s++ && *s);
       return s - p;
    }
    Last edited by cc0d3r; 08-25-2003 at 02:24 PM.
    $ENV: FreeBSD, gcc, emacs

  11. #11
    ~viaxd() viaxd's Avatar
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    Originally posted by cc0d3r
    Hammer, your code should be:
    Code:
    int mystrlen(char *s)
    {
       const char *p = s;
       while(*s++ && *s);
       return s - p;
    }
    both his and your code works , but his while loop is different

  12. #12
    End Of Line Hammer's Avatar
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    >>Hammer, your code should be:<<
    Why exactly? What is the purpose of the two tests in your code?
    When all else fails, read the instructions.
    If you're posting code, use code tags: [code] /* insert code here */ [/code]

  13. #13
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    Never mind
    $ENV: FreeBSD, gcc, emacs

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