Reading input into a C-style string

Question

I am working on a project for my programming class that requires me to work with strings. The program begins by asking the user to input a phrase. Normally I would declare something such as:

    string phrase;

Then I would use:

    getline(cin,phrase);

However, the professor told the class that we aren't allowed to use the string class, we must use only c-based strings. I could be wrong but I believe that c-based strings look something like this:

    char phrase[12] = "hello world";

If this is what my professor means by c-based strings, then I do not know how to input a phrase into them. When I attempt this, the program only stores the first word of the phrase and stops at the first space it sees. For example:

    char phrase[12];

    cin >> phrase;

//input: hello world

    cout << phrase;

//output: hello

Any advice would help and would be greatly appreciated, thank you.

`However, the professor told the class that we aren't allowed to use the string class, we must use only c-based strings.` This is why more and more students are going to Java and other languages and going away from C++. Stupid rules like this... — PaulMcKenzie, Sep 15 '14 at 20:34
Note that "hello world" is 12 characters, not 11. Don't forget the terminating null character. — indiv, Sep 15 '14 at 20:34
thank you I was typing too fast and wasn't being careful. And also I thought that [11] held 12 positions since it started with 0? — BCRwar1, Sep 15 '14 at 20:40
Your professor is giving very dangerous advise to your class. — 5gon12eder, Sep 15 '14 at 20:41
@PaulMcKenzie I'd say it depends on *when* in the course it happens. At a certain level, a C++ developer should be capable of working with C-style strings. — Angew is no longer proud of SO, Sep 15 '14 at 20:44
@Angew Yeah, I'm only in programming 2. The professor doesn't frown upon string class he just wants us to be able to be able to do it this way as well. — BCRwar1, Sep 15 '14 at 20:49
`phrase[11]` holds 11 positions, indexed starting at 0 and ending at 10. — Code-Apprentice, Sep 15 '14 at 20:49
Okay @Code-Apprentice , you're right, I'm still learning haha. — BCRwar1, Sep 15 '14 at 20:53
Rather than use `char phrase[12] = "hello world";`, better to use `char phrase[] = "hello world";` and let the compiler right size the array. — chux - Reinstate Monica, Sep 15 '14 at 21:06

score 4 · Accepted Answer · edited May 23 '17 at 11:45

4

You need to use cin.getline(var_id, var_length) and not cin >> var_id, which actually stops storing the input in the variable when it encounters a space or a new line.

If you want to know more about cin.getline and what problems its use can cause, you can have a look to this post: Program skips cin.getline()

edited May 23 '17 at 11:45

Community

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answered Sep 15 '14 at 20:32

nbro

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Okay thank you, but how do I come up with the "var_length" if I don't know what the user will type in as the phrase? – BCRwar1 Sep 15 '14 at 20:42
1

Specify the buffer/array length. Create an array large enough, in your opinion. – nbro Sep 15 '14 at 20:43
@BCRwar1 `var_length` is the amount of input that you can accept. The user is allowed to type less than this. This is one of the limitations of using a fixed-sized array rather than the `string` class. – Code-Apprentice Sep 15 '14 at 20:50
@Code-Apprentice I have one last question. The next part of the program is a for loop that runs through the phrase one position at a time and stops when it gets to the end of the phrase. Example: for(int k = 0; k < length ; k++ ) { phrase[k]; } I guess my question is, how do I determine length? – BCRwar1 Sep 15 '14 at 21:00
It ends when *i >= length*. If you want that the loop ends when the inputted phrase is finished, you could use this loop codition: *phrase[k] != '\0'*, because, remember, any c-string, to be such, has to terminate with a null-terminated character. – nbro Sep 15 '14 at 21:04

score 1 · Answer 2 · answered Sep 15 '14 at 22:36

If you are reading input into a static char array you can use sizeof(charArray) to determine its maximum lengh. But take into consideration that the last symbol will be end of line, so you can read maximum length-1 symbols into this array.

char phrase[12] ;
cin.getline(phrase, sizeof(phrase));

Reading input into a C-style string

2 Answers2