QtCore Module

Detailed Description

The QtCore module contains non-GUI functionality.

All other PyQt modules rely on this module. To import the module use, for example, the following statement:

from PyQt4 import QtCore

Type Documentation

The input hook can cause problems for certain types of application, particularly those that provide a similar facility through different means. This function removes the input hook installed by PyQt.

 int absoluteValue;
 int myValue = -4;

 absoluteValue = qAbs(myValue);
 // absoluteValue == 4

The checksum is independent of the byte order (endianness).

This function takes a format string and a list of arguments, similar to the C printf() function.

Example:

 void load(const QString &fileName)
 {
     QFile file(fileName);
     if (!file.exists())
         qCritical("File '%s' does not exist!", qPrintable(fileName));
 }

If you include <QtDebug>, a more convenient syntax is also available:

 qCritical() << "Brush:" << myQBrush << "Other
 value:" << i;

A space is inserted between the items, and a newline is appended at the end.

Warning: The internal buffer is limited to 8192 bytes, including the '\0'-terminator.

If you pass the function a format string and a list of arguments, it works in similar way to the C printf() function.

Example:

 qDebug("Items in list: %d", myList.size());

If you include <QtDebug>, a more convenient syntax is also available:

 qDebug() << "Brush:" << myQBrush << "Other value:" << i;

This syntax automatically puts a single space between each item, and outputs a newline at the end. It supports many C++ and Qt types.

Warning: The internal buffer is limited to 8192 bytes, including the '\0'-terminator.

For a release library this function will exit the application with return value 1. For the debug version this function will abort on Unix systems to create a core dump, and report a _CRT_ERROR on Windows allowing to connect a debugger to the application.

This function takes a format string and a list of arguments, similar to the C printf() function.

Example:

 int divide(int a, int b)
 {
     if (b == 0)                                // program error
         qFatal("divide: cannot divide by zero");
     return a / b;
 }

Warning: The internal buffer is limited to 8192 bytes, including the '\0'-terminator.

The message handler is a function that prints out debug messages, warnings, critical and fatal error messages. The Qt library (debug version) contains hundreds of warning messages that are printed when internal errors (usually invalid function arguments) occur. If you implement your own message handler, you get total control of these messages.

The default message handler prints the message to the standard output under X11 or to the debugger under Windows. If it is a fatal message, the application aborts immediately.

Only one message handler can be defined, since this is usually done on an application-wide basis to control debug output.

To restore the message handler, call qInstallMsgHandler(0).

Example:

 #include <qapplication.h>
 #include <stdio.h>
 #include <stdlib.h>

 void myMessageOutput(QtMsgType type, const char *msg)
 {
     switch (type) {
     case QtDebugMsg:
         fprintf(stderr, "Debug: %s\n", msg);
         break;
     case QtWarningMsg:
         fprintf(stderr, "Warning: %s\n", msg);
         break;
     case QtCriticalMsg:
         fprintf(stderr, "Critical: %s\n", msg);
         break;
     case QtFatalMsg:
         fprintf(stderr, "Fatal: %s\n", msg);
         abort();
     }
 }

 int main(int argc, char **argv)
 {
     qInstallMsgHandler(myMessageOutput);
     QApplication app(argc, argv);
     ...
     return app.exec();
 }

Returns a value between 0 and RAND_MAX (defined in <cstdlib> and <stdlib.h>), the next number in the current sequence of pseudo-random integers.

Use qsrand() to initialize the pseudo-random number generator with a seed value.

This function was introduced in Qt 4.2.

 qreal valueA = 2.3;
 qreal valueB = 2.7;

 int roundedValueA = qRound(valueA);
 \\ roundedValueA = 2
 int roundedValueB = qRound(valueB);
 \\ roundedValueB = 3

 qreal valueA = 42949672960.3;
 qreal valueB = 42949672960.7;

 int roundedValueA = qRound(valueA);
 \\ roundedValueA = 42949672960
 int roundedValueB = qRound(valueB);
 \\ roundedValueB = 42949672961

Compares str1 and str2. Returns a negative value if str1 is less than str2, 0 if str1 is equal to str2 or a positive value if str1 is greater than str2.

Special case 1: Returns 0 if str1 and str2 are both 0.

Special case 2: Returns a random non-zero value if str1 is 0 or str2 is 0 (but not both).

This function assumes that dst is large enough to hold the contents of src.

Allocates space for a copy of src, copies it, and returns a pointer to the copy. If src is 0, it immediately returns 0.

Ownership is passed to the caller, so the returned string must be deleted using delete[].

Compares str1 and str2 ignoring the case of the characters. The encoding of the strings is assumed to be Latin-1.

Returns a negative value if str1 is less than str2, 0 if str1 is equal to str2 or a positive value if str1 is greater than str2.

Special case 1: Returns 0 if str1 and str2 are both 0.

Special case 2: Returns a random non-zero value if str1 is 0 or str2 is 0 (but not both).

Returns the number of characters that precede the terminating '\0', or 0 if str is 0.

Compares at most len bytes of str1 and str2.

Returns a negative value if str1 is less than str2, 0 if str1 is equal to str2 or a positive value if str1 is greater than str2.

Special case 1: Returns 0 if str1 and str2 are both 0.

Special case 2: Returns a random non-zero value if str1 is 0 or str2 is 0 (but not both).

Copies at most len bytes from src (stopping at len or the terminating '\0' whichever comes first) into dst and returns a pointer to dst. Guarantees that dst is '\0'-terminated. If src or dst is 0, returns 0 immediately.

This function assumes that dst is at least len characters long.

Compares at most len bytes of str1 and str2 ignoring the case of the characters. The encoding of the strings is assumed to be Latin-1.

Returns a negative value if str1 is less than str2, 0 if str1 is equal to str2 or a positive value if str1 is greater than str2.

Special case 1: Returns 0 if str1 and str2 are both 0.

Special case 2: Returns a random non-zero value if str1 is 0 or str2 is 0 (but not both).

 QString FriendlyConversation.greeting(int type)
 {
     static const char *greeting_strings[] = {
         QT_TR_NOOP("Hello"),
         QT_TR_NOOP("Goodbye")
     };
     return tr(greeting_strings[type]);
 }

The macro expands to sourceText.

 static const char *greeting_strings[] = {
     QT_TRANSLATE_NOOP("FriendlyConversation", "Hello"),
     QT_TRANSLATE_NOOP("FriendlyConversation", "Goodbye")
 };

 QString FriendlyConversation.greeting(int type)
 {
     return tr(greeting_strings[type]);
 }

 QString global_greeting(int type)
 {
     return qApp->translate("FriendlyConversation",
                            greeting_strings[type]);
 }

The macro expands to sourceText.

This function takes a format string and a list of arguments, similar to the C printf() function.

Example:

 void f(int c)
 {
     if (c > 200)
         qWarning("f: bad argument, c == %d", c);
 }

If you include <QtDebug>, a more convenient syntax is also available:

 qWarning() << "Brush:" << myQBrush << "Other value:"
 << i;

This syntax inserts a space between each item, and appends a newline at the end.

Warning: The internal buffer is limited to 8192 bytes, including the '\0'-terminator.