how do I populate a structure containing a ptr with user input?

This is a discussion on how do I populate a structure containing a ptr with user input? within the C++ Programming forums, part of the General Programming Boards category; The following code sets up an array of structures that is partially populated. one of the members is a pointer ...

  1. #1
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    Question how do I populate a structure containing a ptr with user input?

    The following code sets up an array of structures that is partially populated. one of the members is a pointer to a string (lunch[i].name). How do I populate the rest of the structure by user input? A 'for loop' causes a runtime error.


    #include <iostream>
    #include <cstdlib>
    #include <iomanip>
    using namespace std;

    struct food
    {
    char *name;
    int weight, calories;
    };
    const int MAXITEMS = 5;
    void printList(food *lunch);

    int main()
    {
    food lunch[MAXITEMS] = // see note 9.3
    {
    {"apple", 4, 100},
    {"salad", 2, 80},
    };

    lunch[2].name = "onion";
    lunch[2].weight = 1;
    lunch[2].calories = 40; // This works: compiles and printList prints it.



    printList(lunch);

    return 0;
    }

    void printList(food *lunch)
    {
    cout << " Food Name Ounces Cal" << endl;
    cout << " --------- ------ ---" << endl;
    for(int j = 0; j < 3/*MAXITEMS*/; j++)
    cout << setw(15) << lunch[j].name << " "
    << setw(6) << lunch[j].weight << " "
    << setw(5) << lunch[j].calories << endl;

    return;
    }
    rc7j

  2. #2
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    You need to allocate space
    Code:
    char temp[100];
    cin >> temp;  // or cin.getline(temp,100);
    
    // now allocate space and copy
    lunch[i].name = new char[strlen(temp)+1];
    strcpy( lunch[i].name, temp );
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  3. #3
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    thanks. that works. Now how do I allocate space without specifying the length of the string - like making a ragged array? ref. the '*name' pointer in the struct definition.
    Last edited by rc7j; 11-05-2001 at 04:17 PM.
    rc7j

  4. #4
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    using an array of c_style strings I don't think you can. You could with a list of your own design or from STL. STL would also allow you to create a vector of strings (STL strings, not c_style strings), which is the other way I can think of doing this.

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