QLatin1String Class
The QLatin1String class provides a thin wrapper around an US-ASCII/Latin-1 encoded string literal. More...
Header: | #include <QLatin1String> |
qmake: | QT += core |
Note: All functions in this class are reentrant.
Public Types
typedef | difference_type |
typedef | size_type |
Public Functions
int | rbegin() const |
bool | operator!=(const QString &s) const |
bool | operator!=(const char *s) const |
bool | operator!=(const QByteArray &s) const |
bool | operator<(const QString &s) const |
bool | operator<(const char *s) const |
bool | operator<(const QByteArray &s) const |
bool | operator<=(const QString &s) const |
bool | operator<=(const char *s) const |
bool | operator<=(const QByteArray &s) const |
bool | operator==(const char *s) const |
bool | operator==(const QByteArray &s) const |
bool | operator>(const QString &s) const |
bool | operator>(const char *s) const |
bool | operator>(const QByteArray &s) const |
bool | operator>=(const QString &s) const |
bool | operator>=(const char *s) const |
bool | operator>=(const QByteArray &s) const |
Public Variables
int | const_iterator |
Related Non-Members
bool | operator!=(int s1, int s2) |
bool | operator==(int s1, int s2) |
Detailed Description
The QLatin1String class provides a thin wrapper around an US-ASCII/Latin-1 encoded string literal.
Many of QString's member functions are overloaded to accept const char *
instead of QString. This includes the copy constructor, the assignment operator, the comparison operators, and various other functions such as insert(), replace(), and indexOf(). These functions are usually optimized to avoid constructing a QString object for the const char *
data. For example, assuming str
is a QString,
if (str == "auto" || str == "extern" || str == "static" || str == "register") { ... }
is much faster than
if (str == QString("auto") || str == QString("extern") || str == QString("static") || str == QString("register")) { ... }
because it doesn't construct four temporary QString objects and make a deep copy of the character data.
Applications that define QT_NO_CAST_FROM_ASCII
(as explained in the QString documentation) don't have access to QString's const char *
API. To provide an efficient way of specifying constant Latin-1 strings, Qt provides the QLatin1String, which is just a very thin wrapper around a const char *
. Using QLatin1String, the example code above becomes
if (str == QLatin1String("auto") || str == QLatin1String("extern") || str == QLatin1String("static") || str == QLatin1String("register") { ... }
This is a bit longer to type, but it provides exactly the same benefits as the first version of the code, and is faster than converting the Latin-1 strings using QString::fromLatin1().
Thanks to the QString(QLatin1String) constructor, QLatin1String can be used everywhere a QString is expected. For example:
QLabel *label = new QLabel(QLatin1String("MOD"), this);
Note: If the function you're calling with a QLatin1String argument isn't actually overloaded to take QLatin1String, the implicit conversion to QString will trigger a memory allocation, which is usually what you want to avoid by using QLatin1String in the first place. In those cases, using QStringLiteral may be the better option.
See also QString, QLatin1Char, QStringLiteral, and QT_NO_CAST_FROM_ASCII.
Member Type Documentation
typedef QLatin1String::difference_type
Alias for int
. Provided for compatibility with the STL.
This typedef was introduced in Qt 5.10.
typedef QLatin1String::size_type
Alias for int
. Provided for compatibility with the STL.
This typedef was introduced in Qt 5.10.