Qt 5.9 | Qt Core | C++ Classes | QLatin1String

Qt 5.9.9 Reference Documentation

# 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

- List of all members, including inherited members

Note: All functions in this class are reentrant.

## Public Functions

| QLatin1String()
| QLatin1String(const char *str)
| QLatin1String(const char *str, int size)
| QLatin1String(const QByteArray &str)
QLatin1Char | at(int pos) const
const char * | data() const
const char * | latin1() const
QLatin1String | left(int length) const
QLatin1String | mid(int start) const
QLatin1String | mid(int start, int length) const
QLatin1String | right(int length) const
int | size() const
bool | operator!=(const QString &other) const
bool | operator!=(const char *other) const
bool | operator!=(const QByteArray &other) const
bool | operator<(const QString &other) const
bool | operator<(const char *other) const
bool | operator<(const QByteArray &other) const
bool | operator<=(const QString &other) const
bool | operator<=(const char *other) const
bool | operator<=(const QByteArray &other) const
bool | operator==(const QString &other) const
bool | operator==(const char *other) const
bool | operator==(const QByteArray &other) const
bool | operator>(const QString &other) const
bool | operator>(const char *other) const
bool | operator>(const QByteArray &other) const
bool | operator>=(const QString &other) const
bool | operator>=(const char *other) const
bool | operator>=(const QByteArray &other) const
QLatin1Char | operator[](int pos) const

## Related Non-Members

bool | operator!=(QLatin1String s1, QLatin1String s2)
bool | operator<(QLatin1String s1, QLatin1String s2)
bool | operator<=(QLatin1String s1, QLatin1String s2)
bool | operator==(QLatin1String s1, QLatin1String s2)
bool | operator>(QLatin1String s1, QLatin1String s2)
bool | operator>=(QLatin1String s1, QLatin1String 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, and QStringLiteral.

## Member Function Documentation

### QLatin1String::QLatin1String()

Constructs a QLatin1String object that stores a nullptr.

This function was introduced in Qt 5.6.

### QLatin1String::QLatin1String(const char *str)

Constructs a QLatin1String object that stores str.

The string data is not copied. The caller must be able to guarantee that str will not be deleted or modified as long as the QLatin1String object exists.

See also latin1().

### QLatin1String::QLatin1String(const char *str, int size)

Constructs a QLatin1String object that stores str with size.

The string data is not copied. The caller must be able to guarantee that str will not be deleted or modified as long as the QLatin1String object exists.

See also latin1().

### QLatin1String::QLatin1String(const QByteArray &str)

Constructs a QLatin1String object that stores str.

The string data is not copied. The caller must be able to guarantee that str will not be deleted or modified as long as the QLatin1String object exists.

See also latin1().

### QLatin1Char QLatin1String::at(int pos) const

Returns the character at position pos in this object.

Note: This function performs no error checking. The behavior is undefined when pos < 0 or pos >= size().

This function was introduced in Qt 5.8.

See also operator[]().

### const char *QLatin1String::data() const

Returns the Latin-1 string stored in this object.

### const char *QLatin1String::latin1() const

Returns the Latin-1 string stored in this object.

### QLatin1String QLatin1String::left(int length) const

Returns the substring of length length starting at position 0 in this object.

Note: This function performs no error checking. The behavior is undefined when length < 0 or length > size().

This function was introduced in Qt 5.8.

See also mid() and right().

### QLatin1String QLatin1String::mid(int start) const

Returns the substring starting at position start in this object, and extending to the end of the string.

Note: This function performs no error checking. The behavior is undefined when start < 0 or start > size().

This function was introduced in Qt 5.8.

See also left() and right().

### QLatin1String QLatin1String::mid(int start, int length) const

This is an overloaded function.

Returns the substring of length length starting at position start in this object.

Note: This function performs no error checking. The behavior is undefined when start < 0, length < 0, or start + length > size().

This function was introduced in Qt 5.8.

See also left() and right().

### QLatin1String QLatin1String::right(int length) const

Returns the substring of length length starting at position size() - length in this object.

Note: This function performs no error checking. The behavior is undefined when length < 0 or length > size().

This function was introduced in Qt 5.8.

See also mid() and left().

### int QLatin1String::size() const

Returns the size of the Latin-1 string stored in this object.

### bool QLatin1String::operator!=(const QString &other) const

Returns `true` if this string is not equal to string other; otherwise returns `false`.

The comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-interface strings with QString::localeAwareCompare().

### bool QLatin1String::operator!=(const char *other) const

This function overloads operator!=().

The other const char pointer is converted to a QString using the QString::fromUtf8() function.

You can disable this operator by defining `QT_NO_CAST_FROM_ASCII` when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

This function was introduced in Qt 4.3.

### bool QLatin1String::operator!=(const QByteArray &other) const

This function overloads operator!=().

The other byte array is converted to a QString using the QString::fromUtf8() function.

You can disable this operator by defining `QT_NO_CAST_FROM_ASCII` when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

This function was introduced in Qt 5.0.

### bool QLatin1String::operator<(const QString &other) const

Returns `true` if this string is lexically less than the other string; otherwise returns `false`.

The comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-interface strings using the QString::localeAwareCompare() function.

### bool QLatin1String::operator<(const char *other) const

This is an overloaded function.

The other const char pointer is converted to a QString using the QString::fromUtf8() function.

You can disable this operator by defining `QT_NO_CAST_FROM_ASCII` when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

This function was introduced in Qt 4.3.

### bool QLatin1String::operator<(const QByteArray &other) const

This is an overloaded function.

The other const char pointer is converted to a QString using the QString::fromUtf8() function.

You can disable this operator by defining `QT_NO_CAST_FROM_ASCII` when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

This function was introduced in Qt 5.0.

### bool QLatin1String::operator<=(const QString &other) const

Returns `true` if this string is lexically less than or equal to string other; otherwise returns `false`.

The comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-interface strings with QString::localeAwareCompare().

### bool QLatin1String::operator<=(const char *other) const

This is an overloaded function.

The other const char pointer is converted to a QString using the QString::fromUtf8() function.

You can disable this operator by defining `QT_NO_CAST_FROM_ASCII` when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

This function was introduced in Qt 4.3.

### bool QLatin1String::operator<=(const QByteArray &other) const

This is an overloaded function.

The other array is converted to a QString using the QString::fromUtf8() function.

You can disable this operator by defining `QT_NO_CAST_FROM_ASCII` when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

This function was introduced in Qt 5.0.

### bool QLatin1String::operator==(const QString &other) const

Returns `true` if this string is equal to string other; otherwise returns `false`.

The comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-interface strings with QString::localeAwareCompare().

### bool QLatin1String::operator==(const char *other) const

This is an overloaded function.

The other const char pointer is converted to a QString using the QString::fromUtf8() function.

You can disable this operator by defining `QT_NO_CAST_FROM_ASCII` when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

This function was introduced in Qt 4.3.

### bool QLatin1String::operator==(const QByteArray &other) const

This is an overloaded function.

The other byte array is converted to a QString using the QString::fromUtf8() function.

You can disable this operator by defining `QT_NO_CAST_FROM_ASCII` when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

This function was introduced in Qt 5.0.

### bool QLatin1String::operator>(const QString &other) const

Returns `true` if this string is lexically greater than string other; otherwise returns `false`.

The comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-interface strings with QString::localeAwareCompare().

### bool QLatin1String::operator>(const char *other) const

This is an overloaded function.

The other const char pointer is converted to a QString using the QString::fromUtf8() function.

You can disable this operator by defining `QT_NO_CAST_FROM_ASCII` when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

This function was introduced in Qt 4.3.

### bool QLatin1String::operator>(const QByteArray &other) const

This is an overloaded function.

The other const char pointer is converted to a QString using the QString::fromUtf8() function.

You can disable this operator by defining `QT_NO_CAST_FROM_ASCII` when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

This function was introduced in Qt 5.0.

### bool QLatin1String::operator>=(const QString &other) const

Returns `true` if this string is lexically greater than or equal to string other; otherwise returns `false`.

The comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-interface strings with QString::localeAwareCompare().

### bool QLatin1String::operator>=(const char *other) const

This is an overloaded function.

The other const char pointer is converted to a QString using the QString::fromUtf8() function.

You can disable this operator by defining `QT_NO_CAST_FROM_ASCII` when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

This function was introduced in Qt 4.3.

### bool QLatin1String::operator>=(const QByteArray &other) const

This is an overloaded function.

The other array is converted to a QString using the QString::fromUtf8() function.

You can disable this operator by defining `QT_NO_CAST_FROM_ASCII` when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

This function was introduced in Qt 5.0.

### QLatin1Char QLatin1String::operator[](int pos) const

Returns the character at position pos in this object.

Note: This function performs no error checking. The behavior is undefined when pos < 0 or pos >= size().

This function was introduced in Qt 5.8.

See also at().

## Related Non-Members

### bool operator!=(QLatin1String s1, QLatin1String s2)

Returns `true` if string s1 is lexically unequal to string s2; otherwise returns `false`.

### bool operator<(QLatin1String s1, QLatin1String s2)

Returns `true` if string s1 is lexically smaller than string s2; otherwise returns `false`.

### bool operator<=(QLatin1String s1, QLatin1String s2)

Returns `true` if string s1 is lexically smaller than or equal to string s2; otherwise returns `false`.

### bool operator==(QLatin1String s1, QLatin1String s2)

Returns `true` if string s1 is lexically equal to string s2; otherwise returns `false`.

### bool operator>(QLatin1String s1, QLatin1String s2)

Returns `true` if string s1 is lexically greater than string s2; otherwise returns `false`.

### bool operator>=(QLatin1String s1, QLatin1String s2)

Returns `true` if string s1 is lexically greater than or equal to string s2; otherwise returns `false`.