about the use of a string in an ifstream statement

[Herv? LEBAIL]

Hi everybody,

I'm writing a program which use the <string>, <vector> and <ifstream>
classes.

Given an array of string, i.e vector<string> file_names, example :

file_names[0] = "file1.txt"
file_names[1] = "file2.txt"
etc ...

I want to do a for-loop and read the content of all of this files, I
started with (n_file is the size of the dynamical allocated array
file_names) :

for (in_file = 0; in_file < n_file; ++in_file)
{
ifstream file(file_names[in_file],ios::in);
// here the data handling of the content of the file
file.close();
}

It doesn't work, I get a message error during the compiling process
(gnu gcc comiler on linux) :

opt_main.c++:26 1: error: no matching function for call to `
std::basic_ifst ream<char, std::char_trait s<char> >::basic_ifstre am(
std::string&, const std::_Ios_Openm ode&)'
/usr/local/bin/gcc3_3/include/c++/3.3/iosfwd:89: error: candidates
are:
std::basic_ifst ream<char, std::char_trait s<char>[color=blue]
>::basic_ifstre am(const[/color]
std::basic_ifst ream<char, std::char_trait s<char> >&)
/usr/local/bin/gcc3_3/include/c++/3.3/fstream:519: error:
std::basic_ifst ream<_CharT, _Traits>::basic _ifstream(const char*,
std::_Ios_Openm ode = std::ios_base:: in) [with _CharT = char,
_Traits =
std::char_trait s<char>]
/usr/local/bin/gcc3_3/include/c++/3.3/fstream:504: error:
std::basic_ifst ream<_CharT, _Traits>::basic _ifstream() [with _CharT
= char,
_Traits = std::char_trait s<char>]

It's (I guess) probably due to the use of a string or the absence of
quotes in :

ifstream file(file_names[in_file],ios::in);

I've tested instead ifstream
file("\""+file_ names[in_file]+"\"",ios::i n), the quotes are then
present in the string but It still doesn't work.

I've checked that ifstream file("file1.txt ",ios::in) is OK for (one
after the others) all the files.

If soeone has got an idea ...

Thanks in advance

Herve

[Victor Bazarov]

Re: about the use of a string in an ifstream statement

"Herv? LEBAIL" <lebail_herve@h otmail.com> wrote...[color=blue]
> I'm writing a program which use the <string>, <vector> and <ifstream>
> classes.[/color]

Have you actually looked at what 'ifstream's constructor needs?
[color=blue]
>
> Given an array of string, i.e vector<string> file_names, example :
>
> file_names[0] = "file1.txt"
> file_names[1] = "file2.txt"
> etc ...
>
> I want to do a for-loop and read the content of all of this files, I
> started with (n_file is the size of the dynamical allocated array
> file_names) :
>
> for (in_file = 0; in_file < n_file; ++in_file)
> {
> ifstream file(file_names[in_file],ios::in);
> // here the data handling of the content of the file
> file.close();
> }
>
> It doesn't work, I get a message error during the compiling process
> (gnu gcc comiler on linux) :
>
> opt_main.c++:26 1: error: no matching function for call to `
> std::basic_ifst ream<char, std::char_trait s<char> >::basic_ifstre am(
> std::string&, const std::_Ios_Openm ode&)'
> /usr/local/bin/gcc3_3/include/c++/3.3/iosfwd:89: error: candidates
> are:
> std::basic_ifst ream<char, std::char_trait s<char>[color=green]
> >::basic_ifstre am(const[/color]
> std::basic_ifst ream<char, std::char_trait s<char> >&)
> /usr/local/bin/gcc3_3/include/c++/3.3/fstream:519: error:
> std::basic_ifst ream<_CharT, _Traits>::basic _ifstream(const char*,
> std::_Ios_Openm ode = std::ios_base:: in) [with _CharT = char,
> _Traits =
> std::char_trait s<char>]
> /usr/local/bin/gcc3_3/include/c++/3.3/fstream:504: error:
> std::basic_ifst ream<_CharT, _Traits>::basic _ifstream() [with _CharT
> = char,
> _Traits = std::char_trait s<char>]
>
> It's (I guess) probably due to the use of a string or the absence of
> quotes in :[/color]

No, it's not due to absence of quotes. It's due to the fact that
ifstream needs 'const char*' as the first argument of the constructor
and you're shoving it 'string'.
[color=blue]
>
> ifstream file(file_names[in_file],ios::in);
>
> I've tested instead ifstream
> file("\""+file_ names[in_file]+"\"",ios::i n), the quotes are then
> present in the string but It still doesn't work.[/color]

Of course it doesn't work. You need to get 'const char*' out of your
'string' object. To do that use 'c_str()' function:

ifstream file(file_names[in_file].c_str());
[color=blue]
>
> I've checked that ifstream file("file1.txt ",ios::in) is OK for (one
> after the others) all the files.[/color]

Of course it's OK. The string literal (not to be confused with
an object of type 'std::string') has the type "const char[]", which
is convertible to "const char*", while an 'std::string' isn't.
[color=blue]
>
> If soeone has got an idea ...[/color]

See above.

V

[Rob Williscroft]

Re: about the use of a string in an ifstream statement

Herv? LEBAIL wrote in news:1373ddb7.0 402090727.329d4 c76
@posting.google .com:
[color=blue]
>
> I'm writing a program which use the <string>, <vector> and <ifstream>
> classes.
>
> Given an array of string, i.e vector<string> file_names, example :
>
> file_names[0] = "file1.txt"
> file_names[1] = "file2.txt"
> etc ...
>
> I want to do a for-loop and read the content of all of this files, I
> started with (n_file is the size of the dynamical allocated array
> file_names) :
>
> for (in_file = 0; in_file < n_file; ++in_file)
> {
> ifstream file(file_names[in_file],ios::in);[/color]

change to:

ifstream file( file_names[in_file].c_str() ,ios::in );

[color=blue]
> // here the data handling of the content of the file
> file.close();
> }
>
> It doesn't work, I get a message error during the compiling process
> (gnu gcc comiler on linux) :
>[/color]

For some reason the ?fstream ctors only take filename arguments
by char const *, not std::string const &, use std::string's c_str()
member function to get the char const * needed.

HTH.

Rob.
--

http://www.victim-prime.dsl.pipex.com/

[Karl Heinz Buchegger]

Re: about the use of a string in an ifstream statement

Herv? LEBAIL wrote:[color=blue]
>
> Hi everybody,
>
> I'm writing a program which use the <string>, <vector> and <ifstream>
> classes.
>
> Given an array of string, i.e vector<string> file_names, example :
>
> file_names[0] = "file1.txt"
> file_names[1] = "file2.txt"
> etc ...
>
> I want to do a for-loop and read the content of all of this files, I
> started with (n_file is the size of the dynamical allocated array
> file_names) :
>
> for (in_file = 0; in_file < n_file; ++in_file)
> {
> ifstream file(file_names[in_file],ios::in);
> // here the data handling of the content of the file[/color]

Well. Look up your documentation of what the first argument to the
constructor can be.
It can be a 'const char *', but not a std::string.
But you can ask a std::string for a const char* by using
it's member function c_str()

ifstream file( file_names[in_file].c_str(), ios::in );


--
Karl Heinz Buchegger
kbuchegg@gascad .at

[Sumit Rajan]

Re: about the use of a string in an ifstream statement


"Herv? LEBAIL" <lebail_herve@h otmail.com> wrote in message
news:1373ddb7.0 402090727.329d4 c76@posting.goo gle.com...[color=blue]
> Hi everybody,
>
> I'm writing a program which use the <string>, <vector> and <ifstream>
> classes.
>
> Given an array of string, i.e vector<string> file_names, example :
>
> file_names[0] = "file1.txt"
> file_names[1] = "file2.txt"
> etc ...
>
> I want to do a for-loop and read the content of all of this files, I
> started with (n_file is the size of the dynamical allocated array
> file_names) :
>
> for (in_file = 0; in_file < n_file; ++in_file)
> {
> ifstream file(file_names[in_file],ios::in);[/color]

ifstream file(file_names[in_file].c_str());


HTH,
Sumit.

[color=blue]
> // here the data handling of the content of the file
> file.close();
> }
>
> It doesn't work, I get a message error during the compiling process
> (gnu gcc comiler on linux) :
>
> opt_main.c++:26 1: error: no matching function for call to `
> std::basic_ifst ream<char, std::char_trait s<char> >::basic_ifstre am(
> std::string&, const std::_Ios_Openm ode&)'
> /usr/local/bin/gcc3_3/include/c++/3.3/iosfwd:89: error: candidates
> are:
> std::basic_ifst ream<char, std::char_trait s<char>[color=green]
> >::basic_ifstre am(const[/color]
> std::basic_ifst ream<char, std::char_trait s<char> >&)
> /usr/local/bin/gcc3_3/include/c++/3.3/fstream:519: error:
> std::basic_ifst ream<_CharT, _Traits>::basic _ifstream(const char*,
> std::_Ios_Openm ode = std::ios_base:: in) [with _CharT = char,
> _Traits =
> std::char_trait s<char>]
> /usr/local/bin/gcc3_3/include/c++/3.3/fstream:504: error:
> std::basic_ifst ream<_CharT, _Traits>::basic _ifstream() [with _CharT
> = char,
> _Traits = std::char_trait s<char>]
>
> It's (I guess) probably due to the use of a string or the absence of
> quotes in :
>
> ifstream file(file_names[in_file],ios::in);
>
> I've tested instead ifstream
> file("\""+file_ names[in_file]+"\"",ios::i n), the quotes are then
> present in the string but It still doesn't work.
>
> I've checked that ifstream file("file1.txt ",ios::in) is OK for (one
> after the others) all the files.
>
> If soeone has got an idea ...
>
> Thanks in advance
>
> Herve[/color]

[David Harmon]

Re: about the use of a string in an ifstream statement

On 9 Feb 2004 07:27:49 -0800 in comp.lang.c++, lebail_herve@ho tmail.com
(Herv? LEBAIL) was alleged to have written:[color=blue]
> ifstream file(file_names[in_file],ios::in);[/color]

ifstream has no constructor that knows std::string. You have to use the
string::c_str() function to convert

ifstream file(file_names[in_file].c_str(),ios::i n);

[DrUg13]

Re: about the use of a string in an ifstream statement

ostringstream results;
//Get file ready
ifstream data;
data.open(fileN ame.c_str());

results << data.rdbuf(); // put entire file into results
data.close(); // close file were done with it
string temp = results.str();

Now the entire file is now in a string object


On 9 Feb 2004 07:27:49 -0800, lebail_herve@ho tmail.com (Herv? LEBAIL)
wrote:
[color=blue]
>Hi everybody,
>
>I'm writing a program which use the <string>, <vector> and <ifstream>
>classes.
>
>Given an array of string, i.e vector<string> file_names, example :
>
>file_names[0] = "file1.txt"
>file_names[1] = "file2.txt"
>etc ...
>
>I want to do a for-loop and read the content of all of this files, I
>started with (n_file is the size of the dynamical allocated array
>file_names) :
>
>for (in_file = 0; in_file < n_file; ++in_file)
> {
> ifstream file(file_names[in_file],ios::in);
>// here the data handling of the content of the file
> file.close();
> }
>
>It doesn't work, I get a message error during the compiling process
>(gnu gcc comiler on linux) :
>
>opt_main.c++:2 61: error: no matching function for call to `
> std::basic_ifst ream<char, std::char_trait s<char> >::basic_ifstre am(
> std::string&, const std::_Ios_Openm ode&)'
>/usr/local/bin/gcc3_3/include/c++/3.3/iosfwd:89: error: candidates
>are:
> std::basic_ifst ream<char, std::char_trait s<char>[color=green]
>>::basic_ifstr eam(const[/color]
> std::basic_ifst ream<char, std::char_trait s<char> >&)
>/usr/local/bin/gcc3_3/include/c++/3.3/fstream:519: error:
> std::basic_ifst ream<_CharT, _Traits>::basic _ifstream(const char*,
> std::_Ios_Openm ode = std::ios_base:: in) [with _CharT = char,
>_Traits =
> std::char_trait s<char>]
>/usr/local/bin/gcc3_3/include/c++/3.3/fstream:504: error:
> std::basic_ifst ream<_CharT, _Traits>::basic _ifstream() [with _CharT
>= char,
> _Traits = std::char_trait s<char>]
>
>It's (I guess) probably due to the use of a string or the absence of
>quotes in :
>
>ifstream file(file_names[in_file],ios::in);
>
>I've tested instead ifstream
>file("\""+file _names[in_file]+"\"",ios::i n), the quotes are then
>present in the string but It still doesn't work.
>
>I've checked that ifstream file("file1.txt ",ios::in) is OK for (one
>after the others) all the files.
>
>If soeone has got an idea ...
>
>Thanks in advance
>
>Herve[/color]