I want to create a std::ifstream using std::string - c++

On Fri, 27 Apr 2007, gidaeyeo wrote:

> Is there any way to create an instance of std::ifstream using
> std::string.
> (through std::ifstream's constructor or assignment operator or
> iterator, etc...)
>
> i.e.
> std::string str = "this is a string";
> std::ifstream ifs = str; //<----- this is a just pseudo code.

Not an ifstream. As the name (cryptically) says, ifstream is a stream for
files.

However, there's a string stream too.

#include <sstream>

std::istringstream iss(str);

You can use it exactly like the file stream, and if you'r always taking
std::istream references you can even use the same code.

Sebastian Redl

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On Apr 27, 11:53 pm, Sebastian Redl <e0226...@stud3.tuwien.ac.at>
wrote:
> On Fri, 27 Apr 2007, gidaeyeo wrote:
....
> > i.e.
> > std::string str = "this is a string";
> > std::ifstream ifs = str; //<----- this is a just pseudo code.
>
> Not an ifstream. As the name (cryptically) says, ifstream is a stream for
> files.
>
> However, there's a string stream too.
>
....
> std::istringstream iss(str);
>
> You can use it exactly like the file stream, and if you'r always taking
> std::istream references you can even use the same code.

To expand on that a bit, here's an example which will let you flexibly
populate your input string:

std:streamstring os;
os << "Arbitrary input.";
std::istringstream is( os.str() );

now read from 'is' as you would any std istream.


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s5n wrote:
> On Apr 27, 11:53 pm, Sebastian Redl <e0226...@stud3.tuwien.ac.at>
> wrote:
>> std::istringstream iss(str);
>>
>> You can use it exactly like the file stream, and if you'r always taking
>> std::istream references you can even use the same code.
>
> To expand on that a bit, here's an example which will let you flexibly
> populate your input string:
>
> std:streamstring os;

You meant std:stringstream here.

> os << "Arbitrary input.";
> std::istringstream is( os.str() );
>
> now read from 'is' as you would any std istream.

Why bother with two string streams? Just use std::stringstream:

std::stringstream ss;
ss << "2 3 5 7 11";
int i;
while (ss >> i) std::cout << i << '\n';

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Seungbeom Kim

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