A newby question on the sizeof operator

This is a discussion on A newby question on the sizeof operator within the C++ Programming forums, part of the General Programming Boards category; letīs say you got this function: void DoSomething( char* mystring) { ........\; whatever; } and you pass an array to ...

  1. #1
    Evo
    Evo is offline
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    A newby question on the sizeof operator

    letīs say you got this function:

    void DoSomething( char* mystring)
    {
    ........\\;
    whatever;
    }

    and you pass an array to it like this:

    char teststring[] = "this is some text";
    DoSomething( teststring );

    how in GODS NAME! can you get the number of elements of the array INSIDE the function?? (without using strlen() ofcourse, or supose the array is of integers)
    iībe tried the usual:
    int mylen = sizeof mystring / sizeof mystring[0];
    but it wont work, my guess is that im getting the size of THE POINTER to the array NOT the array itself.
    i also tried changing the function to take an array NOT a pointer (but of course its the same thing, since only the address of the array gets passed. (right?)

    is there a way to solve this? (not including passing the size to the function as an argument of course)
    thanks.

  2. #2
    Registered User quagsire's Avatar
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    There is no way in C/C++ that I know of. I use the first element of the array to hold the number of elements (like in turbo pascal with strings : string[0] holds length). If you are using char, then it will limit you to 255 elements.

    Code:
    #include <string.h>
    #include <stdlib.h>
    #include <iostream.h>
    
    void doSomething(char *cptr)
    {
       int numElements = cptr[0];
       for (int i = 1; i <= numElements; i++)
       {
          cout << "Element " << i << " = " << cptr[i] << endl;
       }
    }
    
    int main()
    {
       char teststring[] = "this is some text";
       int len = strlen(teststring);
       char * temp = new char[len + 1];
       temp[0] = len;
       strcpy(&temp[1], teststring);
       doSomething(temp);
       delete[] temp;
       return 0;
    }
    This works fine in Borland C++ 5.02. You can also try using list, vector, etc.

  3. #3
    End Of Line Hammer's Avatar
    Join Date
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    6,231
    How about passing a second parameter that denotes the array length to the function.

    >void doSomething(char *cptr, int len)
    When all else fails, read the instructions.
    If you're posting code, use code tags: [code] /* insert code here */ [/code]

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