Find if a shell file exists

Sylas

The program below works very well for the file designed in the path. I should like that it works with the file I ask with a cin.
Many thanks, Here is the file :
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main()
{
cout << "rentrez nom du shell\n";//give me the name of the shell
string shell("");//empty string
cin >> shell;
string path="/home/sylvain/";
string total=path+shell;
total='"'+path+shell+'"';
cout << total <<endl;// Ok jusque là
//ifstream monFlux(total);
ifstream monFlux("/home/sylvain/essai"); //On essaye d'ouvrir le fichier
if(monFlux) cout << "Ce fichier existe\n";
else cout << "fichier inexistant." << endl;
}

jsulm

Why do you post same question again?
One is enough: http://forum.qt.io/topic/65004/find-if-a-shell-file-exists

Sylas

@jsulm I lost my post. I don't know why. My answer was: I don't think it is possible to introduce a string in the middle of a line of a program. Indeed the compiller sends me "Error".

mrjj

@Sylas said:

introduce a string in the middle of a line of a program

Hi its not really clear to me what u mean by that :)

Sylas

@Sylas Look please at the commented line "ifstream". Uncomment that and you'll see computer return ERROR

mrjj

but what was the error`?
The compiler actually tells you what is wrong.
So to be a programmer, u MUST care for what it says. :)

I think it just a case of NOT right type?
ifstream monFlux(total);

here you gives it a std::string
total is a std::string, yes?
does it expect that?

maybe
ifstream monFlux(total.c_str());
will make it more happy?

Sylas

@mrjj It runs well but the if statement is always "inexistant file". The compiler says: Checking for existance: /home/sylvain/ESSAI/bin/Release/ESSAI.
ESSAI is the name of the project (Code:Blocks), but the name of the file is essai.
essai really exists as a shell file. Thanks again, because now we go forth

mrjj

and the file is there
"/home/sylvain/essai" ?

im not sure your code can actually check if file exits since you just create the
stream object but dont really use it.

maybe try
ifstream a_file ( "/home/sylvain/essai" );

if ( !a_file.is_open() ) {
cout << "fichier inexistant." << endl;
}
else {
cout << "Ce fichier existe\n";
}

Sylas

@mrjj I tried your little program. It runs but, unfortunately, gives always the same answer: "ce fichier existe", even if it is not true.

Sylas

@mrjj Excuse me. Your litte program works very well. I did the mistake to not replace essai by an other file (inexistent), inside your little program.

mrjj

ok that sounds good. :)
a_file.is_open() should only be true when it can actually open the file. (it exists)

Sylas

@mrjj I tried that: ifstream a_file("/home/sylvain/" <<shell<<'"'); The compiler says: error no match for 'oprator <<' (operand types are 'const char [15] and 'std::string {aka std::basic_string<char>}')
As I am a beginner that is chinese for me, but for you it is different.

mrjj

@Sylas said:

a_file("/home/sylvain/" <<shell<<'"');

this syntax is not valid.
you cannot use << this way.

you would do something like

string filename;
cin >> filename;
string path="/home/sylvain/";
string fullpath=path+filename;
fstream a_file (fullpath );
if ( !a_file.is_open() ) {
....

Sylas

@mrjj May be the solution is much more simple. I tried that:
cout << "rentrez nom du fichier\n";
string a_file;
cin >> a_file;

if ( !a_file.is_open() ) {
cout << "fichier inexistant." << endl;
}
else {
cout << "Ce fichier existe\n";
}
My new error is: 'std::string' has no member named 'is_open'
What do you think of that ? ? Many thanks

mrjj

hi
The open function belong to fstream class
and in this case the compiler is very clear :)

'std::string' has no member named 'is_open'

Which means that
string a_file; <---- its a string
do not have such function.

fstream has it
http://www.cplusplus.com/reference/fstream/ifstream/is_open/

so it will never work.

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