1.12. Identifiers, Types, and Literals

1.12. Identifiers, Types, and Literals
	Chapter 1. C++ Introduction

[ fromfile: cppintro.xml id: idliterals ]

Identifiers are names that are used in C++ programs

An identifier consists of a sequence of letters, digits, and underscores that does not begin with a digit.
An identifier cannot be a reserved keyword. See Appendix A C++ Reserved Keywords for a list of them.

A literal is a constant value that appears somewhere in a program.
Because every value has a type, every literal has a type also.
Table 1.1 shows some examples of literals and their types.

Table 1.1. Examples of Literals

Literal	Meaning
5	`int` literal
5u	`u` or `U` specifies unsigned int
5L	l or L specifies `long int` after an integer
05	Octal `int` literal
0x5	Hexadecimal `int` literal
true	`bool` literal
5.0F	f or F specifies single precision `float`ing point literal
5.0	`double` precision floating point literal
5.0L	l or L specifies `long double` if it comes after a floating point
'5'	`char` literal (ASCII 53)
"50"	`const char*` containing the chars `'5' '0'` and `'\0'`
"any" "body"	"anybody"
'\a'	Alert
'\\'	Backslash
'\b'	Backspace
'\r'	Return (or Enter)
'\''	Single quote
'\"'	Double quote
'\f'	Formfeed (newpage)
'\t'	Tab
'\n'	Newline `char` literal
"\n"	Newline followed by null terminator (`const char*`)
'\0'	Null character
'\v'	Vertical tab
"a string with newline\n"	Another `const char*`

Example 1.17 shows how certain characters need to be escaped inside double-quoted string delimiters.

Example 1.17. src/early-examples/literals/qliterals.cpp

#include <QTextStream>
#include <QString>

int main() {
    const char* charstr = "this is one very long string "
                " so I will continue it on the next line";
    QTextStream cout(stdout);  
    QString str = charstr; 
    cout << str << endl;
    cout << "\nA\tb\\c\'d\"" << endl;
    return 0;
}

C-style strings can be converted to QString.

Building and running this program produce the following output.

src/early-examples/literals> qmake -project
src/early-examples/literals> qmake
src/early-examples/literals> make
g++ -c -pipe -O2 -Wall -W -D_REENTRANT -DQT_NO_DEBUG -DQT_GUI_LIB
  -DQT_CORE_LIB -DQT_SHARED -I/usr/share/qt4/mkspecs/linux-g++ -I.
  -I/usr/include/qt4/QtCore -I/usr/include/qt4/QtCore
  -I/usr/include/qt4/QtGui -I/usr/include/qt4/QtGui
  -I/usr/include/qt4 -I. -I. -I. -o qliterals.o qliterals.cpp
g++ -o literals qliterals.o  -L/usr/lib -lQtGui -lQtCore -lpthread
src/early-examples/literals> ./literals

The output should look something like this:

this is one very long string so I will continue it on the next line

A       b\c'd"


1.11.1. Exercises: Qt Dialogs for User Input/Output		1.12.1. Exercises: Identifiers, Types, and Literals