Find if a shell file exists



  • 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;
    }


  • Moderators

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



  • @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".


  • Qt Champions 2016

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


  • Qt Champions 2016

    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?



  • @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


  • Qt Champions 2016

    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";
    }



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



  • @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.


  • Qt Champions 2016

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



  • @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.


  • Qt Champions 2016

    @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() ) {
    ....



  • @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


  • Qt Champions 2016

    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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