invalid conversion from `char*' to `char'

This is a discussion on invalid conversion from `char*' to `char' within the C Programming forums, part of the General Programming Boards category; This is a snippet of code Code: FROM THE MAIN FUNCTION: Push(s1,check,line); /*s1 is a structure with elements Element *contents; ...

  1. #1
    Ron
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    invalid conversion from `char*' to `char'

    This is a snippet of code
    Code:
    FROM THE MAIN FUNCTION:
    
    Push(s1,check,line); /*s1 is a structure with elements 	Element *contents;
                                                            int top;
    	                                                int lineST;
                          check is a string array
                          line is an integer */
    
    PUSH FUNCTION ACCESSED FROM ANOTHER C FILE:
    
    void Push(stackST *stackP, char* element, int line)
    {
    
      /* Put information in array; update top. */
      char newelement[20];
      int i=0;
      int length = strlen(element);
      for (i=0;i<=length;i++)
    	newelement[i++]=putchar(*element++);
      newelement[i] = '/0';
     stackP->contents[++stackP->top] = newelement;
      stackP->lineST=line;
    }
    I get the following warning and error for the line marked in bold
    warning: multi-character character constant
    error:invalid conversion from `char*' to `char'

    I have twisted the code a lot. But cant figure the solution to this problem.
    Last edited by Ron; 06-14-2008 at 11:30 AM.

  2. #2
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    Apparently Element::contents is a char pointer or char array, and when indexing that, you get a char. Newelement is a char array.
    It is too clear and so it is hard to see.
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  3. #3
    Ron
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    yes you are right, contents is a pointer.
    hmmm....
    so what would the syntax be if i were to point it to newelement?

  4. #4
    and the Hat of Guessing tabstop's Avatar
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    (1) The null character is \0, not /0.
    (2) If you want to change the pointer, just use the pointer. I have no idea what pointer you're trying to change -- stackP[top].contents, perhaps?

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    and the hat of wrongness Salem's Avatar
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    > for (i=0;i<=length;i++)
    > newelement[i++]=putchar(*element++);
    Why does this increment i twice each time?

    > stackP->contents[++stackP->top] = newelement;
    Assuming you fix the left to be a char*, you're still pointing at a local variable - this is a big no-no

    You need to use malloc to allocate newelement if you want it to persist longer than the life of this function.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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  6. #6
    Ron
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    Re:

    I have already done so when initializing the stack
    Code:
    void StackInit(stackST *stackP)
    {
      stackElement *newContents;
    
      /* Allocate a new array to hold the contents. */
    
      newContents = (stackElement *)malloc(sizeof(stackElement) * 10);
    
      stackP->contents = newContents;
      stackP->lineST = 0;
      stackP->top = -1;  /* I.e., empty */
    }
    Thanks for pointing out about the increment.

  7. #7
    and the hat of wrongness Salem's Avatar
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    What's a stackElement
    Perhaps you're meant to strcpy it?
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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  8. #8
    Ron
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    stackelement is a type-defined character defined.

    Also, for some reason the error now doesnt show up anymore in the push function.
    But the error comes up in the line of code that calls the push function.
    Code:
    Push(s1,check,line); /*s1 is a structure with elements 	Element *contents;
                                                            int top;
    	                                                int lineST;
                          check is a string array
                          line is an integer */
    error: invalid conversion from `char*' to `stackElement'
    error: initializing argument 2 of `void Push(stackST*, stackElement, int)'

  9. #9
    and the Hat of Guessing tabstop's Avatar
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    Apparently stackElement is not a char *. So again: what is it?

  10. #10
    Ron
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    I get so impatient with UNIX.......

    I dont know what the 2nd argument is supposed to be a string.
    I dont know why it refers to stackelement

  11. #11
    and the Hat of Guessing tabstop's Avatar
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    This has nothing to do with UNIX and everything to do with your program. Look at your function: void Push(stackST*, stackElement, int). That second argument says stackElement. How did you define stackElement, and what do you want it to be?

  12. #12
    Ron
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    I figured what went wrong. I gave the wrong parameter in the explicit function call in the header file. Thanks for your help.

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