Qt Coding Style

This is a overview of the coding convention we use when writing Qt code. The data has been gathered by mining the Qt sources, discussion forums, email threads and through collaboration of the developers.

Indentation

• 4 spaces are used for indentation
• Spaces, not tabs!

Declaring variables

• Declare each variable on a separate line
• Avoid short (e.g., a,rbarr,nughdeget) names whenever possible
• Single character variable names are only okay for counters and temporaries, where the purpose of the variable is obvious
• Wait with declaring a variable until it is needed

    // Wrong
    int a, b;
    char *c, *d;

    // Correct
    int height;
    int width;
    char *nameOfThis;
    char *nameOfThat;

• Variables and functions start with a small letter. Each consecive word in a variable's name starts with a capital letter
• Avoid abbreviations

    // Wrong
    short Cntr;
    char ITEM_DELIM = '\t';

    // Correct
    short counter;
    char itemDelimiter = '\t';

• Classes always start with a big letter. Public classes start with a 'Q' (QRgb). Public functions most often start with a 'q' (qRgb).

Whitespace

• Use blank lines to group statements together where suited
• Always use only one blank line
• Always use a single space after a keyword, and before a curly brace.

    // Wrong
    if(foo){
    }

    // Correct
    if (foo) {
    }

• For pointers or references, always use a single space before '*' or '&', but never after.
• No space after a cast.
• Avoid C-style casts when possible.

    // Wrong
    char* blockOfMemory = (char* ) malloc(data.size());

    // Correct
    char *blockOfMemory = (char *)malloc(data.size());
    char *blockOfMemory = reinterpret_cast<char *>(malloc(data.size()));

Braces

• As a base rule, the left curly brace goes on the same line as the start of the statement:

    // Wrong
    if (codec)
    {
    }

    // Correct
    if (codec) {
    }

• Exception: Function implementations and class declarations always have the left brace on the start of a line:

    static void foo(int g)
    {
        qDebug("foo: %i", g);
    }

    class Moo
    {
    };

• Use curly braces when the body of a conditional statement contains more than one line, and also if a single line statement is somewhat complex.

    // Wrong
    if (address.isEmpty()) {
        return false;
    }

    for (int i = 0; i < 10; ++i) {
        qDebug("%i", i);
    }

    // Correct
    if (address.isEmpty())
        return false;

    for (int i = 0; i < 10; ++i)
        qDebug("%i", i);

• Exception 1: Use braces also if the parent statement covers several lines / wraps

    // Correct
    if (address.isEmpty() || !isValid()
        || !codec) {
        return false;
    }

• Exception 2: Use braces also in if-then-else blocks where either the if-code or the else-code covers several lines

    // Wrong
    if (address.isEmpty())
        return false;
    else {
        qDebug("%s", qPrintable(address));
        ++it;
    }

    // Correct
    if (address.isEmpty()) {
        return false;
    } else {
        qDebug("%s", qPrintable(address));
        ++it;
    }

Switch statements

• The case labels are on the same column as the switch
• Every case must have a break (or return) statement at the end or a comment to indicate that there's intentionally no break

    switch (myEnum) {
    case Value1:
        doSomething();
        break;
    case Value2:
        doSomethingElse();
        // fall through
    default:
        defaultHandling();
        break;
    }

Line breaks

• Keep lines shorter than 100 characters; insert line breaks if necessary.

General exception

• Feel free to break a rule if it makes your code look bad.