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Pradeep
Guest
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 Posted: Thu Oct 19, 2006 9:10 am Post subject: Problem | Istream_iterator in std::copy |
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Hi All,
I am facing some problem using istream_iterator for reading the
contents of a file and copying it in a vector of strings.However the
same thing works for a vector of integers.
The code that doesn't work is
std::vector<std::string> vecStr;
std::ifstream fstrRead("Test.txt");
if(!fstrRead)
{
std::cerr<<"Cannot Read the file"<<std::endl;
exit(-1);
}
std::copy(std::istream_iterator<std::string>(fstrRead),
std::istream_iterator<std::string> (),
std::back_inserter(vecStr));
The problem is in std::istream_iterator<std::string> (). The
constructor calls the method
void _Getval()
{ // get a _Ty value if possible
if (_Myistr != 0 && !(*_Myistr >> _Myval))
_Myistr = 0;
}
where it fails in conversion.
The compiler error is c:\Program Files\Microsoft Visual Studio .NET
2003\Vc7\include\iterator(213): error C2679: binary '>>' : no operator
found which takes a right-hand operand of type 'std::string' (or there
is no acceptable conversion)
However this works fine if it is an vector of integers.
vector<int> vi;//vector to be filled
ifstream vi_dump("vi.txt"); //open for read
if (!vi_dump)
{
cerr<<"couldn't open file";
exit(1);
}
copy(istream_iterator<int> (vi_dump),
istream_iterator<int> (),
back_inserter(vi));
I would like to know the reason for this and how it can be solved?
Thanks in Advance,
Pradeep |
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Sumit Rajan
Guest
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| Posted: Thu Oct 19, 2006 9:10 am Post subject: Re: Problem | Istream_iterator in std::copy |
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|
Pradeep wrote:
| Quote: | Hi All,
I am facing some problem using istream_iterator for reading the
contents of a file and copying it in a vector of strings.However the
same thing works for a vector of integers.
The code that doesn't work is
std::vector<std::string> vecStr;
std::ifstream fstrRead("Test.txt");
if(!fstrRead)
{
std::cerr<<"Cannot Read the file"<<std::endl;
exit(-1);
}
std::copy(std::istream_iterator<std::string>(fstrRead),
std::istream_iterator<std::string> (),
std::back_inserter(vecStr));
|
Well you'll need to post the actual program(a minimal version that
demonstrates your problem). Please see:
http://www.parashift.com/c++-faq-lite/how-to-post.html
Try compiling:
#include <iostream>
#include <string>
#include <fstream>
#include <vector>
int main()
{
std::vector<std::string> vecStr;
std::ifstream fstrRead("Test.txt");
if(!fstrRead)
{
std::cerr<<"Cannot Read the file"<<std::endl;
exit(-1);
}
std::copy(std::istream_iterator<std::string>(fstrRead),
std::istream_iterator<std::string> (),
std::back_inserter(vecStr));
}
It compiles for me on both VC++ and Comeau. I suspect that it a case of
your missing out on an #include.
Regards,
Sumit. |
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Piyush
Guest
|
| Posted: Thu Oct 19, 2006 9:10 am Post subject: Re: Problem | Istream_iterator in std::copy |
|
|
Pradeep wrote:
| Quote: | Hi All,
I am facing some problem using istream_iterator for reading the
contents of a file and copying it in a vector of strings.However the
same thing works for a vector of integers.
The code that doesn't work is
std::vector<std::string> vecStr;
std::ifstream fstrRead("Test.txt");
if(!fstrRead)
{
std::cerr<<"Cannot Read the file"<<std::endl;
exit(-1);
}
std::copy(std::istream_iterator<std::string>(fstrRead),
std::istream_iterator<std::string> (),
std::back_inserter(vecStr));
The problem is in std::istream_iterator<std::string> (). The
constructor calls the method
void _Getval()
{ // get a _Ty value if possible
if (_Myistr != 0 && !(*_Myistr >> _Myval))
_Myistr = 0;
}
where it fails in conversion.
The compiler error is c:\Program Files\Microsoft Visual Studio .NET
2003\Vc7\include\iterator(213): error C2679: binary '>>' : no operator
found which takes a right-hand operand of type 'std::string' (or there
is no acceptable conversion)
However this works fine if it is an vector of integers.
vector<int> vi;//vector to be filled
ifstream vi_dump("vi.txt"); //open for read
if (!vi_dump)
{
cerr<<"couldn't open file";
exit(1);
}
copy(istream_iterator<int> (vi_dump),
istream_iterator<int> (),
back_inserter(vi));
I would like to know the reason for this and how it can be solved?
Thanks in Advance,
Pradeep
|
Hey,
The problem with your code is that the string class has a friend
function which handles reading and writing it from a stream.(the >> and
<< operators). Now since this function is declared in the string header
once you include this header the code compiles.
Regards,
Piyush |
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