assign string to int array

This is a discussion on assign string to int array within the C++ Programming forums, part of the General Programming Boards category; Hi all, I am new to C++.Any help would be appreciated. I have the following code: int myArray[20]; string str= ...

  1. #1
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    assign string to int array

    Hi all,

    I am new to C++.Any help would be appreciated.

    I have the following code:

    int myArray[20];
    string str= "1,2,3,8,10,12";

    I would like to assign str to myArray in that a way that the result will be as follow:
    myArray[0] = 1
    myArray[1] = 2
    myArray[2] = 3
    myArray[3] = 8
    myArray[4] = 10
    myArray[5] = 12

    May I know how to do that?I have try many times but unable to get the desired result. Thank you.

  2. #2
    and the hat of sweating
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    You can try strtok(), then assign each result to each element of the int array.
    "I am probably the laziest programmer on the planet, a fact with which anyone who has ever seen my code will agree." - esbo, 11/15/2008

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  3. #3
    C++ Witch laserlight's Avatar
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    Unfortunately, strtok() does not play well with std::string.

    One idea is that given a string like "1 2 3 8 10 12", it is easy to do what you want to do: initialise a stringstream with that string, then use operator>> to extract the numbers in a loop. Thus, you can change the format of your input string to this format simply by replacing the commas with spaces.
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    and instead of a c-style array of integers, I'd recommend a vector. it automatically performs bounds checking, and resizes itself automatically if you put too many items in it.

  5. #5
    spurious conceit MK27's Avatar
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    Hey I picked up a C++ book at the library yesterday

    So I thought one thing to do here would be create a class derived from string so you could add a "extract_number(pos)" method, but...
    Code:
    class nlist : public string {
    	string str;
    	public:
    		nlist(string in) {
    			str.assign(in);
    		}
    };
    The resulting object does not seem to have inherited much, I guess because the std::string methods don't refer to my "string str"?

    How can you/should you do this?
    C programming resources:
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    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

  6. #6
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by MK27
    So I thought one thing to do here would be create a class derived from string so you could add a "extract_number(pos)" method
    That is a bad idea: std::string is not designed/intended to be a public base class. Ironically, a correct solution is what you are used to in C: create a non-member non-friend function.
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  7. #7
    spurious conceit MK27's Avatar
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    Hey well I'm getting closer:
    Code:
    class nlist : public string {
    	public:
    		nlist(string in) {
    			assign(in);
    		}
    };
    Works.
    Quote Originally Posted by laserlight
    That is a bad idea: std::string is not designed/intended to be a public base class.
    So what is bad about it?
    Last edited by MK27; 02-22-2010 at 11:33 AM.
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

  8. #8
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by MK27
    So what is bad about it?
    Conceptually, it is bad because you are just publicly inheriting to reuse an implementation, since std::string has no virtual functions to override. It makes the use of this function more difficult: to use it properly, you need an object of the derived class, yet one might want to use the function with std::string objects.

    Furthermore, in the event that an object of nlist is destroyed through a std::string pointer, undefined behaviour will result since std::string does not have a virtual destructor.

    You could inherit privately instead, but then users of your class will not have access to the various string functions unless you re-expose them.
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  9. #9
    spurious conceit MK27's Avatar
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    Quote Originally Posted by laserlight View Post
    Conceptually, it is bad because you are just publicly inheriting to reuse an implementation, since std::string has no virtual functions to override. It makes the use of this function more difficult: to use it properly, you need an object of the derived class, yet one might want to use the function with std::string objects.
    Okay, well I agree with that: it is probably not a good idea from a design point of view, just wanted to make sure it was not flawed in a more profound sense.

    Furthermore, in the event that an object of nlist is destroyed through a std::string pointer, undefined behaviour will result since std::string does not have a virtual destructor.
    So avoid doing that, is what you are saying.
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

  10. #10
    and the hat of sweating
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    Quote Originally Posted by laserlight View Post
    Unfortunately, strtok() does not play well with std::string.
    Doh! I thought it was a char* array. That's what happens when I'm in a rush.
    "I am probably the laziest programmer on the planet, a fact with which anyone who has ever seen my code will agree." - esbo, 11/15/2008

    "the internet is a scary place to be thats why i dont use it much." - billet, 03/17/2010

  11. #11
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    Smile Problem solved

    Hi all

    Thank for your reply and help.I have solved it by using stringstream as suggested by laserlight .

    Cheer!1

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