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

c++file-existsqt

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.

Best Solution

(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.

This is the source code to check 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 no 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

(with 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 no 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 no directory?
bool fileExists = QFileInfo::exists(path) && QFileInfo(path).isFile();