struct problem

autome2005 · #1 07-Nov-2005, 06:23

hi,

i have to manipulate two strings and i have to use a structure. The problem that i am having is that i can't read the second string. I don't know what is wrong with this code. Can anyone help.

thanks.

here is a sample of my code.

CPP / C++ / C Code:

#include <iostream>
#include <string.h>
#include <cctype>
#include <cstdlib>
#include <cmath>
#include <iomanip>

using namespace std;

struct text {
       char *strLine;
       int strLength;
       void readString();
};

void text::readString(){
     char textTemp[100];
     
     cout << "\n\nenter string: ";
     cin.getline(textTemp, 100);
     cout << "\nenter length: ";
     cin >> strLength;
     
     strLine = new char[strLength + 1];
     strLine[0] = 0;
     strcpy(strLine, textTemp);
}

void display(text & text){
     cout << "\nYour string: " << text.strLine << endl;
}


int main(){
    text myString, myString2;
    
    myString.readString();
    display(myString); 
    myString2.readString();
    display(myString2);
    
    delete [] myString.strLine;
    delete [] myString2.strLine;
    
    return 0;
}

davekw7x · #2 07-Nov-2005, 06:59

Quote:

Originally Posted by autome2005

hi,

i have to manipulate two strings and i have to use a structure. The problem that i am having is that i can't read the second string.

getline() reads chars from the stream buffer up, to but not including, the terminating character. The terminating character is a newline. So the first call to getline reads your first string but leaves the '\n' in the stream buffer.

The next call for input (with "cin >>" ) is for a number. Now, for reading numbers with >>, leading whitespace is ignored, so the program gets the newline from the stream buffer and ignores it and waits until it sees something numerical in the stream buffer. In other words it waits for user input.

When the user enters a number, the >> operator gets the numerical digits from the stream buffer and stops taking items from the stream buffer when it sees something that is not part of a number (the newline in this case). In other words the newline is still in the stream buffer.

Now for your second string: the getline() sees the newline left over from the last "cin>>" and returns with no characters and leaves the newline in the stream buffer. The program continues and gets the number from the user. That's why string 2 is always empty.

One easy way to make sure the '\n' is cleared after reading the number is to put something like something like this in your readString() function:

CPP / C++ / C Code:

void text::readString()
{
     char textTemp[100];
     
     cout << "\n\nenter string: ";
     cin.getline(textTemp, 100);
     cout << "\nenter length: ";
     cin >> strLength;

     cin.ignore(100, '\n'); // clear newline from buffer for next getline()
     
     strLine = new char[strLength + 1];
     strLine[0] = 0;
     strcpy(strLine, textTemp);
}

Actually, this is not perfect, but it's a way to get started.

A better way is to use something like this:

CPP / C++ / C Code:

     std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');

You have to #include <limits.h> for this.

This and other interesting things can be found here: Parashift C++ FAQ

Regards,

Dave

Paramesh · #3 07-Nov-2005, 07:08

Hi autome,

There is no need to get the length of the string from the user.
You can calculate it by yourself.

There are two ways.
One is by using the strlen function.
The other way is to calculate the length by using a loop.

Using strlen function:

CPP / C++ / C Code:

    char *strLine = "Hello there";
    int strLength;
 
    strLength = strlen(strLine);
    
    cout << "The length of " << strLine << " is " << strLength << endl;

The other way is to calculate by using a loop.
here is a sample code:

CPP / C++ / C Code:

    char *strLine = "Hello there";
    int strLength = 0;
 
    for( ; strLine[ strLength ] ; strLength++ )
    ;
    
    cout<<"The length of "<<strLine<<" is "<<strLength<<endl;

Now, on to the program:

First, #include <string.h> must be replaced by

CPP / C++ / C Code:

#include <cstring>

because in C++, string.h is a depreciated header file.

Then, instead of getting the length from the user, you can modify the readString function like this:

CPP / C++ / C Code:

void text::readString()
{
     char textTemp[100];

     cout << "\n\nenter string: ";
     cin.getline(textTemp, 100);

     strLength = strlen(textTemp);

     strLine = new char[strLength + 1];
     strcpy(strLine, textTemp);

}

and you can modify your display function like this:

CPP / C++ / C Code:

void display(text mystring)
{
     cout << "\nYour string: " << mystring.strLine << endl;
}

because there is no need for &
and dont use variable names same as the struct name. So, vary your name like mystring.

One more way to improve your program:
Instead of havind display as a separate function, you can have a function in the struct itself.
so, what we have to do now add a function in the text declaration ,like this:

CPP / C++ / C Code:

struct text
{
       char *strLine;        //string
       int strLength;        //string length
       void readString();    //function to read the string
       void display();       //function to display the string 
};

and make the display function like this:

CPP / C++ / C Code:

void text::display()
{
     cout << "\nYour string: " << strLine << endl;
}

Summarising the program is:

CPP / C++ / C Code:

#include <iostream>
#include <cstring>

using namespace std;

struct text
{
       char *strLine;        //string
       int strLength;        //string length
       void readString();    //function to read the string
       void display();       //function to display the string 
};

void text::readString()
{
     char textTemp[100];

     cout << "\n\nenter string: ";
     cin.getline(textTemp, 100);

     strLength = strlen(textTemp);

     strLine = new char[strLength + 1];
     strcpy(strLine, textTemp);
}

void text::display()
{
     cout << "\nYour string: " << strLine << endl;
}


int main()
{
    text myString, myString2;     //two text objects

    myString.readString();        //get the input
    myString.display();           //display the string
    myString2.readString();
    myString2.display();

    delete [] myString.strLine;
    delete [] myString2.strLine;

    return 0;
}

Please insert your c++ code between [noparse][c++] and [/c++] [noparse] tags.
Dont forget to read the [url="http://www.gidforums.com/t-5566.html"]Guidelines[/url].
Thank you.

Regards,

Paramesh.

autome2005 · #4 07-Nov-2005, 08:11

thank You Dave once again You saved my life.

autome2005 · #5 07-Nov-2005, 08:14

thank You Dave once again You saved my life.

and thanks Paramesh for your comments, yes i know about the length functions but in my project i have to ask a user for sting length.

automne2005

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