Thread: structures and string

RE-EDIT: this whole post is inaccurate. maybe i should quit drinkin

try this
cout << strncpy(&first.name, &first.name, 20);


besides first.name[20] will only hold 20 characters anyway - that include the '\0'


EDIT: the following is inaccurate
cin knows how many characters name can hold, and will only write up to that many characters - 1. the -1 is '\0'. well, actually, cin will write that one too

Correction: cin will resize your character arrays

....i just re-read your original post - it doesn't make much sense

How can I do to printout the name up to 20 and ignore the rest. As is, if the name is more than 20 character will printout up to 20 and ends the program.

just what exactly do you want?

In the program below, what if name of the company is larger than 20 characters.

Your program will either crash when you try to output the name, or you will get a bunch of junk characters after the name. If you want to know why, see my post in this thread:

http://cboard.cprogramming.com/showthread.php?t=63956

How can I do to printout the name up to 20 and ignore the rest.

Like this:

Code:

char name[20];
cout<<"enter a name: ";
cin.getline(name, 20);  //standard method of reading data into a char array
	
cout<<name<<endl;

Note: getline() will read in 19 chars and put a '\0' in the last position of the array. The '\0' is necessary to output char arrays using cout<<. If you want to read in 20 chars, then make your array size 21, and put 21 in getline(). If the user enters less than 20 chars, then getline() will put a '\0' after the last character of input, and only the number of chars read in will be output when you use cout<<.

i was wrong - cin will resize character arrays - i'm not sure what i was thinking.

perhaps you want to use char * name; rather than char name[20];

i was wrong - cin will resize character arrays

Nope. Read the link I posted for more info. strlen() is going out of bounds. <cstring> functions only work on cstrings, i.e. char arrays that end with a '\0'. All <cstring> functions use loops to traverse the char array, and the '\0' indicates the end of the char array:

Code:

int i = 0;
while(theCharArray[i] != '\0')
{
     //do something with theCharArray
     i++;
}

The <<operator does the same thing to output char arrays. There is no array bounds checking in C++, so you can go out of bounds and C++ will not complain.

If the user enters more than 20 chars, then the >>operator will happily fill the entire array with input, so there will be no terminating '\0'. If there are less than 20 chars, it looks like the >>operator enters a '\0' after the last char of the input, so the <<operator will display the output correctly.

Therefore, you don't use the >>operator, e.g. cin>>, to read input into char arrays.

ha - i should know better than to use VC to test my code

MS-VC++ 6.0
code:

Code:

#include <iostream>

using namespace std;

int main()
{
	char * name;
	cout << '>';
	cin >> name;
	cout << name << ' ' << strlen(name) << endl;

	char *p = name;
	while(*p)
	{
		cout << *p;
		p++;
	}
	cout << endl;

	return 0;
}

output:

Code:

>abcdefg
abcdefg 7
abcdefg
Press any key to continue

Dev-c++ seg faults

Thank you every one for answer.

The problem is that if I type more than 20 characters the program will just print out the name up to 20, and that is fine, but will ignore the rest of the program

Example: if I change "cin" for "cin.get(first.name, 10)"

Company name
This test is only with 10 characters

Enter the pizza diameter

Enter the pizza weight


Your Pizza Company name is: This test
The diameter of the pizza is: 0 Inches
The weight of the pizza is: 0 Pounds

Press any key to continue

It jumps the diameter and weight and prints out "0" for both.

Example using a name with less than 10 characters

Company name
Nine

Enter the pizza diameter
23

Enter the pizza weight
34


Your Pizza Company name is: Nine
The diameter of the pizza is: 23 Inches
The weight of the pizza is: 34 Pounds

Press any key to continue

If the person that is typing does not know that the limit is 20(or 10) will type a name more than the limit and the rest of the program will not execute

The reason this happens is because the get will extract the first 9 characters from the stream "This test" and will leave the remainder still in the stream. Then when you ask for the pizza diameter (which is a float), cin will attempt to process the remainder of what is left in the input stream, the " is only with 10 characters" part. The problem with this is that cin will go into an error state once it tries to convert "is" into a float and the cin will exit without doing anything, the "is" won't even be extracted from the input stream. Later, you ask the user for the pizza weight and again try to use cin to get this value. But, since cin was put into the error state previously (and is still in an error state), the extraction automatically fails. The effect of this is that it appears to you, the user, that the program is not letting you enter in any input for these two values.

If you expect the user to enter more data than you are going to accept for the name, there are two courses of action you should consider. The best course would be to use a string container instead of a char array to store this information. The string container will allow you to store however much data you need it to.

Code:

#include <string>

...

struct pizza
{
string name;
float diameter;
double weight;
};

...

cout << "Company name\n";
getline(cin,first.name);

If you are set on using a char array, then you should probably call the ignore member function after the first cin.

Code:

#include <limits>

...

cout << "Company name\n";
cin.get(first.name,10);  // Test only getting first 9 characters and skipping rest of input
cin.ignore(numeric_limits<streamsize>::max(),'\n');
cout << "\nEnter the pizza diameter\n";
cin >> first.diameter;

etc...