CODEWITHSUNDEEP
c++qtfile-exists
user1322915
user1322915

Reputation: 1291

How to check whether file exists in Qt in c++

How do I check whether a file exists in a given path or not in Qt?

My current code is below:

QFile Fout("/Users/Hans/Desktop/result.txt");

if(!Fout.exists()) 
{       
  eh.handleError(8);
}  
else
{
  // ......
}

But when I run the code it is not giving the error message specified in handleError even though the file I mentioned in the path does not exist.

Upvotes: 88

Views: 103701

Answers (5)

mozzbozz
mozzbozz

Reputation: 3143

(TL;DR at the bottom)

I would use the QFileInfo class (docs) – this is exactly what it is made for:

The QFileInfo class provides system-independent file information.

QFileInfo provides information about a file's name and position (path) in the file system, its access rights and whether it is a directory or symbolic link, etc. The file's size and last modified/read times are also available. QFileInfo can also be used to obtain information about a Qt resource.

Here is a function which checks whether a file exists:

#include <QFileInfo>

(don't forget to add the corresponding #include statement)

bool fileExists(QString path) {
    QFileInfo check_file(path);
    // check if file exists and if yes: Is it really a file and not a directory?
    if (check_file.exists() && check_file.isFile()) {
        return true;
    } else {
        return false;
    }
}

Also consider: Do you only want to check if the path exists (exists()) or do you want to also make sure that this is a file and not a directory (isFile())?

Be careful: The documentation of the exists() function says:

Returns true if the file exists; otherwise returns false.

Note: If file is a symlink that points to a non-existing file, false is returned.

This is not precise. It should be:

Returns true if the path (i.e. file or directory) exists; otherwise returns false.

TL;DR

(a shorter version of the function above, saving a few lines of code)

#include <QFileInfo>

bool fileExists(QString path) {
    QFileInfo check_file(path);
    // check if path exists and if yes: Is it really a file and not a directory?
    return check_file.exists() && check_file.isFile();
}

TL;DR for Qt >=5.2

(using exists as a static which was introduce in Qt 5.2; the docs say the static function is faster, though I'm not sure this is still the case when also using the isFile() method; at least this is a one-liner then)

#include <QFileInfo>

// check if path exists and if yes: Is it a file and not a directory?
bool fileExists = QFileInfo::exists(path) && QFileInfo(path).isFile();

Upvotes: 113

Donald Duck
Donald Duck

Reputation: 8892

You can use the QFileInfo::exists() static method:

#include <QFileInfo>
if(QFileInfo::exists("C:\\exampleFile.txt")){
    //The file exists
}
else{
    //The file doesn't exist
}

If you want it to return true only if the file exists and false if the path exists but is a folder, you can combine it with QDir::exists():

#include <QFileInfo>
#include <QDir>
QString path = "C:\\exampleFile.txt";
if(QFileInfo::exists(path) && !QDir(path).exists()){
    //The file exists and is not a folder
}
else{
    //The file doesn't exist, either the path doesn't exist or is the path of a folder
}

Upvotes: 16

Essetee
Essetee

Reputation: 63

That's how I check if the database exists:

#include <QtSql>
#include <QDebug>
#include <QSqlDatabase>
#include <QSqlError>
#include <QFileInfo>

QString db_path = "/home/serge/Projects/sqlite/users_admin.db";

QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
db.setDatabaseName(db_path);

if (QFileInfo::exists(db_path))
{
    bool ok = db.open();
    if(ok)
    {
        qDebug() << "Connected to the Database !";
        db.close();
    }
}
else
{
    qDebug() << "Database doesn't exists !";
}

With SQLite it's difficult to check if the database exists, because it automatically creates a new database if it doesn't exist.

Upvotes: 3

Anthony
Anthony

Reputation: 8788

The code you've posted is correct. Chances are that something else is wrong.

Try putting this:

qDebug() << "Function is being called.";

inside of your handleError function. If the above message prints, you know something else is the problem.

Upvotes: 8

Jerry Coffin
Jerry Coffin

Reputation: 490148

I would skip using anything from Qt at all, and just use the old standard access: 

if (0==access("/Users/Hans/Desktop/result.txt", 0))
    // it exists
else
    // it doesn't exist

Upvotes: 1

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