C++ – How to set precise size of QPushButton

cqtqt5user interface

I have SignatureEditorForm class, which inherits QDialog class:

SignatureEditorForm(QWidget* parent_widget) : QDialog(parent_widget)
{
    resize(SIGNATURE_EDITOR_SIZE);
    setWindowTitle(QString("Signature Editor"));
    setWindowFlags(Qt::Window | Qt::MSWindowsFixedSizeDialogHint | Qt::WindowCloseButtonHint);
    setModal(true);
    {
        QPushButton* const button = new QPushButton(QString("<"), this);
        const QSize BUTTON_SIZE = QSize(22, 22);
        button->resize(BUTTON_SIZE);
    }
}

It contains QPushButton which has size (width: 22, height: 22) and "<" caption.
I have such picture of this widget (SignatureEditorForm). QPushButton has size (width: 20, height: 20). How can I set precise size of button?

P.S. I tried to use setMinimumSize, but it has not effects.

P.P.S. this line button->setStyleSheet("border: 1px solid black; background: white"); gives such effect (precise size)

Best Answer

QWidget::setFixedSize

This and other methods works fine to set exact size of QWidget.

But your problem is not in Qt, it in Windows Styling.

Actual size of widget is exact, but Windows reserve space on borders for animations, so it looks smaller than you expect.

To fix it you need to write own style like this:

button->setStyleSheet("border: 1px solid black; background: white");

Or use any of styles available here:

http://doc.qt.io/qt-5/gallery.html

Setting a bit

Use the bitwise OR operator (|) to set a bit.

number |= 1UL << n;

That will set the nth bit of number. n should be zero, if you want to set the 1st bit and so on upto n-1, if you want to set the nth bit.

Use 1ULL if number is wider than unsigned long; promotion of 1UL << n doesn't happen until after evaluating 1UL << n where it's undefined behaviour to shift by more than the width of a long. The same applies to all the rest of the examples.

Clearing a bit

Use the bitwise AND operator (&) to clear a bit.

number &= ~(1UL << n);

That will clear the nth bit of number. You must invert the bit string with the bitwise NOT operator (~), then AND it.

Toggling a bit

The XOR operator (^) can be used to toggle a bit.

number ^= 1UL << n;

That will toggle the nth bit of number.

Checking a bit

You didn't ask for this, but I might as well add it.

To check a bit, shift the number n to the right, then bitwise AND it:

bit = (number >> n) & 1U;

That will put the value of the nth bit of number into the variable bit.

Changing the nth bit to x

Setting the nth bit to either 1 or 0 can be achieved with the following on a 2's complement C++ implementation:

number ^= (-x ^ number) & (1UL << n);

Bit n will be set if x is 1, and cleared if x is 0. If x has some other value, you get garbage. x = !!x will booleanize it to 0 or 1.

To make this independent of 2's complement negation behaviour (where -1 has all bits set, unlike on a 1's complement or sign/magnitude C++ implementation), use unsigned negation.

number ^= (-(unsigned long)x ^ number) & (1UL << n);

unsigned long newbit = !!x;    // Also booleanize to force 0 or 1
number ^= (-newbit ^ number) & (1UL << n);

It's generally a good idea to use unsigned types for portable bit manipulation.

number = (number & ~(1UL << n)) | (x << n);

(number & ~(1UL << n)) will clear the nth bit and (x << n) will set the nth bit to x.

It's also generally a good idea to not to copy/paste code in general and so many people use preprocessor macros (like the community wiki answer further down) or some sort of encapsulation.

C++ – How to iterate over the words of a string

I use this to split string by a delimiter. The first puts the results in a pre-constructed vector, the second returns a new vector.

#include <string>
#include <sstream>
#include <vector>
#include <iterator>

template <typename Out>
void split(const std::string &s, char delim, Out result) {
    std::istringstream iss(s);
    std::string item;
    while (std::getline(iss, item, delim)) {
        *result++ = item;
    }
}

std::vector<std::string> split(const std::string &s, char delim) {
    std::vector<std::string> elems;
    split(s, delim, std::back_inserter(elems));
    return elems;
}

Note that this solution does not skip empty tokens, so the following will find 4 items, one of which is empty:

std::vector<std::string> x = split("one:two::three", ':');