Programming Forums > Application Development > C++

Mcoy · Feb 24th, 2007, 2:37 PM

I am trying to write code that will take a string of 4 numbers separated by 3 spaces and put them into two integer arrays representing the x and y values of two coordinates. ie:
INPUT:
0 0 4 7

coordinate_1[X] = 0
coordinate_1[Y] = 0
coordinate_2[X] = 4
coordinate_2[Y] = 7

Here is the code:

(Toggle Plain Text)

#include <iostream>
#include <string>
#include <sstream>
#include <stdlib.h>

using namespace std;

int main()
{
    int cor_1[2];
    int cor_2[2];
    
    string input;
    string temp;
    
    stringstream StrToInt;
    
    getline(cin, input);
    
    StrToInt << input[0];
    StrToInt >> cor_1[0];
    
    StrToInt << input[2];
    StrToInt >> cor_1[1];
    
    StrToInt << input[4];
    StrToInt >> cor_2[0];
    
    StrToInt << input[6];
    StrToInt >> cor_1[1];

    cout << cor_1[0] << cor_1[1] << cor_2[0] << cor_2[1] << "\n";
    
    system("PAUSE");
    
    return 0;
    
}

I figured that I could add x to the stream, read x from the stream, add y to the stream, read y from the stream etc. The output for the program is incorrect though, the only correct value ends up being cor_1[0]. All the others seem to be random numbers of great length.
What is it about the above code or my understanding of stringstreams that is wrong?

DaWei · Feb 24th, 2007, 3:51 PM

Your first transaction exausts the stream and sets the eof bit. That's a sort of fail condition. The stream won't work again for you until you clear that. Here are two good suggestions: 1) read the documentation for the things you use; 2) always test for success when you use those things. Failure is not an uncommon occurrence, particularly when a user is involved.

Mcoy · Feb 24th, 2007, 4:33 PM

I forgot to mention that I had tried StrToInt.clear(), then StrToInt.str("") after it was read. It did not change the result

.
I am not very experienced in c++ and many guides on the STL are confusing. Unfortunately I have a programming competition this Tuesday and I have to focus on concepts, not semantics, although I recognize that normally its good to focus on both.
I'll keep looking for some info, and as always thanks for the quick reply DaWei.

DaWei · Feb 24th, 2007, 6:03 PM

Unfortunately, the value of a concept is sometimes -858993460

.

Mcoy · Feb 24th, 2007, 9:23 PM

I tried messing around with the code again and it turns out using StrToInt.clear() works after all. Must have been a typo somewhere in the code.

What do you mean by "documentation"? Is there something like unix 'man' pages for c++ libraries? The library, google and programmingfourms are the only "documentation" I use right now.

DaWei · Feb 24th, 2007, 9:38 PM

Man pages are good. I sometimes use them. I also use MSDN on line, and have an ancient set of MSDN CDs tied into my help system. In particular, research the >> operator.

Realize that any function that is asked to convert user input to numeric values is wide open for trouble. %x*zh is hard to convert. Users may be inattentive, malicious, unknowing, or merely fall asleep with their forehead on the keyboard. Failing to test operations for success is the hallmark of a novice, at best. It could represent actionable negligence.

jubitzu · Feb 26th, 2007, 5:44 AM

As far as C++ documentation goes, the SGI Standard Template Library Programmer's Guide is about as good as I have found for free online. It is similar to unix man pages for each item in the library.

Feb 24th, 2007, 2:37 PM	#1
Mcoy Newbie Join Date: Mar 2006 Posts: 20 Rep Power: 0	How to reset a stringstream object? I am trying to write code that will take a string of 4 numbers separated by 3 spaces and put them into two integer arrays representing the x and y values of two coordinates. ie: INPUT: 0 0 4 7 coordinate_1[X] = 0 coordinate_1[Y] = 0 coordinate_2[X] = 4 coordinate_2[Y] = 7 Here is the code: (Toggle Plain Text) #include <iostream> #include <string> #include <sstream> #include <stdlib.h> using namespace std; int main() { int cor_1[2]; int cor_2[2]; string input; string temp; stringstream StrToInt; getline(cin, input); StrToInt << input[0]; StrToInt >> cor_1[0]; StrToInt << input[2]; StrToInt >> cor_1[1]; StrToInt << input[4]; StrToInt >> cor_2[0]; StrToInt << input[6]; StrToInt >> cor_1[1]; cout << cor_1[0] << cor_1[1] << cor_2[0] << cor_2[1] << "\n"; system("PAUSE"); return 0; } #include <iostream> #include <string> #include <sstream> #include <stdlib.h> using namespace std; int main() { int cor_1[2]; int cor_2[2]; string input; string temp; stringstream StrToInt; getline(cin, input); StrToInt << input[0]; StrToInt >> cor_1[0]; StrToInt << input[2]; StrToInt >> cor_1[1]; StrToInt << input[4]; StrToInt >> cor_2[0]; StrToInt << input[6]; StrToInt >> cor_1[1]; cout << cor_1[0] << cor_1[1] << cor_2[0] << cor_2[1] << "\n"; system("PAUSE"); return 0; } I figured that I could add x to the stream, read x from the stream, add y to the stream, read y from the stream etc. The output for the program is incorrect though, the only correct value ends up being cor_1[0]. All the others seem to be random numbers of great length. What is it about the above code or my understanding of stringstreams that is wrong?

Feb 24th, 2007, 3:51 PM	#2
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	Your first transaction exausts the stream and sets the eof bit. That's a sort of fail condition. The stream won't work again for you until you clear that. Here are two good suggestions: 1) read the documentation for the things you use; 2) always test for success when you use those things. Failure is not an uncommon occurrence, particularly when a user is involved. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Feb 24th, 2007, 6:03 PM	#4
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	Unfortunately, the value of a concept is sometimes -858993460 . __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Feb 24th, 2007, 9:38 PM	#6
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	Man pages are good. I sometimes use them. I also use MSDN on line, and have an ancient set of MSDN CDs tied into my help system. In particular, research the >> operator. Realize that any function that is asked to convert user input to numeric values is wide open for trouble. %xzh is hard to convert. Users may be inattentive, malicious, unknowing, or merely fall asleep with their forehead on the keyboard. Failing to test operations for success is the hallmark of a novice, at best. It could represent actionable negligence. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers*

Feb 26th, 2007, 5:44 AM	#7
jubitzu Newbie Join Date: May 2005 Location: Colorful Colorado Posts: 25 Rep Power: 0	As far as C++ documentation goes, the SGI Standard Template Library Programmer's Guide is about as good as I have found for free online. It is similar to unix man pages for each item in the library. __________________ How to ask questions the smart way

Feb 24th, 2007, 4:33 PM	#3
Mcoy Newbie Join Date: Mar 2006 Posts: 20 Rep Power: 0	I forgot to mention that I had tried StrToInt.clear(), then StrToInt.str("") after it was read. It did not change the result . I am not very experienced in c++ and many guides on the STL are confusing. Unfortunately I have a programming competition this Tuesday and I have to focus on concepts, not semantics, although I recognize that normally its good to focus on both. I'll keep looking for some info, and as always thanks for the quick reply DaWei.

Feb 24th, 2007, 9:23 PM	#5
Mcoy Newbie Join Date: Mar 2006 Posts: 20 Rep Power: 0	I tried messing around with the code again and it turns out using StrToInt.clear() works after all. Must have been a typo somewhere in the code. What do you mean by "documentation"? Is there something like unix 'man' pages for c++ libraries? The library, google and programmingfourms are the only "documentation" I use right now.

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Programming Forums > Application Development > C++

How to reset a stringstream object?