simple string modification

[markman]

Say i had a string such as:
"1 -2.5 6"
(without the quotes) and I wanted to set the three numbers to a, b, and c. How would I do that?

[saridemir]

I think you have to write a function that input a string and generates array and you can split the string by " " (remember strings are also array). I do not have time now if noone answer your question I will write you an sample code...
yilmaz..

[markman]

yeah but how do I split the string by " "?

[kedaman]

1. while in the string
2. find " "
3. add the substring between the occurances of " " to a list

[parksie]

Also:istringstream iss("5 -2.5 6");

float a, b, c;

iss >> a >> b >> c;

[markman]

istringstream comes from what header file?

[Wynd]

Parksie: what exactly do istringstream and ostringstream do?

[parksie]

#include <strstream>Stringstreams are specialisations of istream and ostream for string objects.

Instead of formatting onto stdout, they format into a string, replacing sprintf and sscanf.

[markman]

how come this wont work then?
make a file Test.in with the text:
3
1 2 1
1 1 1
1 -2.5 6
then put this code in a project:

#include <fstream.h>
#include <iostream.h>
#include <strstream>
struct ABC {
double a;
double b;
double c;
};



void main() {
char* inFilename = "Test.in";
char* outFilename = "Test.out";
ifstream infile(inFilename);
ofstream outfile(outFilename);
char szText[20] = "";
int i = 0;
istringstream splitter = "";
ABC vABC;

while (infile >> szText) {
i++;
if (i > 1) {
/////////////////////////////
splitter = szText;
splitter >> vABC.a >> vABC.b >> vABC.c;
cout << vABC.a << endl;
cout << vABC.b << endl;
cout << vABC.c << endl;
/////////////////////////////
}
}
}

I get 15 errors from the header file.

[CornedBee]

a) to get a complete line of the file you should use getline (the global version)

b) C++ headers with .h are deprecated. You should use the ones without the .h instead. Important: NEVER mix the two types.

c) C++ headers without the .h define everything in the std namespace. You can either
- always use std:: when accessing one of the header elements (e.g. std::cout << "Hello" << std::endl;)
- use using declarations to make specific parts accessible (e.g.
using std::cout;
cout << "Hello" << std::endl; // endl is still not accessible
// you could change that with using std::endl
)
- include the whole namespace by doing
using namespace std;
after including all headers.

This should solve at least 14 of the 15 errors you have.

[markman]

then how come this wont work?
using the same file as im my previous post:

#include <fstream>
#include <iostream>
#include <strstream>
using namespace std;

struct ABC {
double a;
double b;
double c;
};

void main() {
char* inFilename = "Test.in";
char* outFilename = "Test.out";
ifstream infile(inFilename);
ofstream outfile(outFilename);
char szText[20] = "";

int i = 0;
istringstream iss;

ABC vABC;

while (infile.getline(szText,20,' ')) {
i++;
if (i > 1) {
/////////////////////////////
iss = szText;
iss >> vABC.a >> vABC.b >> vABC.c;
cout << vABC.a << endl;
cout << vABC.b << endl;
cout << vABC.c << endl;
/////////////////////////////
}

}

}

[parksie]

iss = szText;Not sure about that one...try creating the istringstream at that point.

What compiler errors/logic problems do you have?

[Wynd]

Originally posted by parksie
Also:istringstream iss("5 -2.5 6");

float a, b, c;

iss >> a >> b >> c; So what exactly does this do?

[markman]

#include <strstream>
using namespace std;

void main() {
istringstream iss("5 -2.5 6");

float a, b, c;

iss >> a >> b >> c;
}

Even this doesnt work

[markman]

bump

Hurry up! I need to know how to do this by february next year!

[parksie]

That's a whole 11 months ;)

I don't have a compiler at the moment so I wouldn't know :(

How about a << iss or something?

[CornedBee]

when I do
istringstream iss;
it gives me this error:
error C2079: 'iss' uses undefined class 'basic_istringstream<char,struct std::char_traits<char>,class std::allocator<char> >'

In the help, istringstream is defined as
typedef basic_istringstream<char> istringstream;
but there is no header file that contains this line. In <strstream> there is the class istrstream, which is derived from istream, which is the char-specialization of basic_istream.
So you probably must use this class.
Here is the modified code (compiles and runs with correct output on my pc):

#include <strstream>
#include <iostream>
using namespace std;

void main()
{
istrstream iss("5 -2.5 6");

float a, b, c;

iss >> a >> b >> c;

cout << a << " " << b << " " << c << endl;
}

[parksie]

Try <sstream> I may have been thinking insanely last time...

istrstream is the old type, don't use it (it's easy to get huge memory leaks if you don't know how it works).

[CornedBee]

Works! Here's your solution markman!

btw parksie, istrstream comes from the new template-based standard library too, why is it bad?

[parksie]

istrstream isn't templated :p

http://www.dinkumware.com/htm_cpl/strstrea.html

[CornedBee]

typedef basic_istream<char, char_traits<char> > istream;
class istrstream : public istream // ...


vs.


template<class _E,
class _Tr = char_traits<_E>,
class _A = allocator<_E> >
class basic_istringstream : public basic_istream<_E, _Tr> // ...
typedef basic_istringstream<char, char_traits<char>, allocator<char> > istringstream;


It's not THAT much difference, both come from basic_istream

[parksie]

Hmmm...didn't look like that when I looked at it.

But either way, stick to the longer version...it makes more difference in output stringstreams:

char* ostrstream::str()

as opposed to

string ostringstream::str()

[CornedBee]

good point
I wish the STL documentation of VC++ was better...

[parksie]

I prefer the dinkumware documentation, it's well good (plus they sell a standard library replacement for visual c++).

[markman]

Ok. How would i get the string from a text file and then split it? I cant seem to be able to set the iss = the text from the text file.....

[parksie]

ifstream file("whatsit.txt");

file >> a >> b >> c;

[markman]

I should have asked that at the beginning :rolleyes:

[parksie]

Dead nice, these streams - they all work in exactly the same way :D

[CornedBee]

I don't see the need to buy an additional STL when I already paid for the VC++ one. (I have all this stuff for private use, no company that pays my programs)

[parksie]

It's called standards compliance, which is a big thing in a corporate environment.

[CornedBee]

Documentation of VC++ Standard Library says i/ostringstream <sstream> is for string objects, i/ostrstream <strstream> is for C-style strings...