How do I find out which suffix user has chosen when using a QFileDialog?

Well I'm using the following code to get the filename for a file that needs to be stored ..

QString fileName = QFileDialog::getSaveFileName(this, tr("Save File"),"/home/user/MyDocs/",tr("JPG files (*.jpg);;BMP files (*.bmp);;PNG files (*.png)"));

I'm providing the user with a number of options regarding the file format in which the file is to be saved. However, the returned QString only give开发者_如何学Gos me the prefix filename the user have chosen, not the suffix and thus I don't know which file format the user chose. How can I detect such a file format?

The code in the question works in Windows (Qt 4.6.2 and Win XP). fileName contains the selected extension. But you are obviously using something else Windows, so you could try this workaround:

QFileDialog dialog(this, tr("Save as ..."), "/home/user/MyDocs/");
dialog.setAcceptMode(QFileDialog::AcceptSave);
QStringList filters;
filters << "JPG files (*.jpg)" << "BMP files (*.bmp)" << "PNG files (*.png)";
dialog.setNameFilters(filters);
if (dialog.exec() == QDialog::Accepted)
{
    QString selectedFilter = dialog.selectedNameFilter();
    QString fileName = dialog.selectedFiles()[0];
}

That is a slighty modified code from here.

You need to use the 5th optional string
I usually do it like this:

#define JPEG_FILES "JPG files (*.jpg)"
#define BMP_FILES "BMP files (*.bmp)"
#define PNG_FILES "PNG files (*.png)"

QString selectedFilter;
QString fileName = QFileDialog::getSaveFileName(this, tr("Save File"),
        "/home/user/MyDocs/",
        JPEG_FILES ";;" BMP_FILES ";;" PNG_FILES, &selectedFilter);

if (fileName.isNull())
  return;
if (selectedFilter == JPEG_FILES) {
  ...
} else if (selectedFilter == BMP_FILES) { 
  ...
} else if (selectedFilter == PNG_FILES) {
  ...
} else {  
    // something strange happened 
}

The compiler takes care to concatenate the literal strings in the argument.

I'm not sure how the returned string interacts with tr(). You'll have to test and find out. probably need to un-translate it.
It could have been nicer if the function would return the index of the selected filter but alas, it does not.

A nicer solution would be to put the filters in a list, create a string from it and then compare to the returned selected filter string to the ones in the list. This would also solve the tr() problem.

Have a look to this discussion. It uses QFileInfo on the string that was entered in a QFileDialog.