Passing string through a function...

This is a discussion on Passing string through a function... within the C++ Programming forums, part of the General Programming Boards category; Howdy. I have been pondering how I would go about taking, in this case, the name of a subject (for ...

  1. #1
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    Question Passing string through a function...

    Howdy. I have been pondering how I would go about taking, in this case, the name of a subject (for a GPA tracking program), and pass it through to an overloaded constructor. I figured pointers were the solution, but nonetheless I kept getting "int to char[11]" errors and the like. Here is a stubbed out version of what I've attempted so far:

    #include <iostream.h>

    class Course
    {

    public:

    Course();
    Course(int pname, float credits, unsigned short sem, unsigned short per);
    ~Course();

    private:

    char courseName[11];
    float creditsAtt;
    unsigned short Semesters;
    unsigned short Period;

    };

    Course::Course()
    {

    }

    Course::Course(int pname, float credits, unsigned short sem, unsigned short per)
    {

    courseName = * pname; // so this should give the string,
    // and courseName is a string
    // identical to the local string
    // in int main(). Where have I
    // fouled things up?
    creditsAtt = credits;
    Semesters = sem;
    Period = per;

    }

    //////////////////////////////////////////////////
    //////////////////////////////////////////////////

    int main()
    {

    char name[11];
    float credits = 0;
    unsigned short sem = 0;
    unsigned short per = 0;

    // ( I deleted a lot of explanation, irrelevant stuff here )

    //////////////////////////////////////////////////
    //////////////////////////////////////////////////

    Course * All = new Course[9];
    Course * pCourse;

    int * pname = 0; // OK, setting a pointer for each string

    for(short p = 0; p < 9; p++)
    {

    cout << "\nPlease enter the name of period number " << p << ", 10 characters max please:\t";

    cin.get(name, 10);

    pname = &name; // OK. So this sets the pointer to name's
    // address, right?

    // ( deleted more irrelevant stuff, questions for info )

    pCourse = new Course(pname, credits, sem, per); // OK, so
    // this should set name's address at pname into the parameter?
    All[p] = * pCourse;
    delete pCourse;
    delete pname; // do I have to do this in this case?

    }

    delete [] All;

    return 0;

    }

    ////////////////////////////////////////////////////////
    ////////////////////////////////////////////////////////

    END OF CODE

    Hey, thanks a billion. Just wondered if anyone could give this a quick scan and detect my obvious error. :-P
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  2. #2
    C++ Developer XSquared's Avatar
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    pname should be char *pname in your main and constructor. Also, use <iostream>, not <iostream.h>
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  3. #3
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    Course(int pname, float credits, unsigned short sem, unsigned short per)

    In your parameter list you are saying pname is of type int. If you declare a parameter to be

    int Mr_Compiler_this_is_a_pointer

    the compiler won't change the type to int*. Similarly, just because you use the name "pname" as your parameter name doesn't mean it's a pointer.
    Last edited by 7stud; 04-15-2003 at 05:06 AM.

  4. #4
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    Unhappy

    Oh okay thanks guys, but I've noticed two snags: when I change it to <iostream>, I get like 33 errors and 3 warnings, saying that basically everything is done incorrectly. also, for some reason when i changed the pointers to char and added pointer designations in main and the constructor, nothing changed.
    Last edited by MisterWonderful; 04-15-2003 at 01:01 PM.

  5. #5
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    Post

    I should change that, I figured out how to use <iostream> w/ using namespace std...

    okay, so I get an error at this particular line of the aforementioned code...

    Course::Course(char *pname, float credits, unsigned short sem, unsigned short per)
    {

    courseName = *pname; // right here. the error code is:

    /*C:\Programs\GPAcalc\beta.cpp(50) : error C2440: '=' : cannot convert from 'char' to 'char [11]'
    There are no conversions to array types, although there are conversions to references or pointers to arrays*/

    creditsAtt = credits;
    Semesters = sem;
    Period = per;

    }

    ///// END CODE

    and I changed the pointer in int main() to char * pname;
    I changed all of the constructor parameters to char * pname.
    When I called the function, I changed it to *pname instead of pname. Sorry to bother you guys with all this stuff, hopefully as soon as I figure out how to pass references correctly I'll be able to write this GPA prog much more smoothly. Thanks!

  6. #6
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    Course::Course(char *pname, float credits, unsigned short sem, unsigned short per)
    {

    courseName = *pname; // right here. the error code is:


    char courseName[11];

    Arrays names act like pointers but they aren't exactly pointers. I cannot explain the internals of why you can't do this:

    char text[10];
    text= "dog";

    but basically it's like a type mismatch "dog" is a string literal that's length is 4(when it's stored in memory a \0 is appended), and text's length is 10. They have to be equal.

    The following code demonstrates that a true pointer can point to cstyle strings of different lengths:

    char* pname;
    pname = "dog";
    pname = "A bigger dog";

    )
    Last edited by 7stud; 04-15-2003 at 02:58 PM.

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