[ fromfile: cppintro.xml id: idliterals ]

Identifiers are names that are used in C++ programs for functions, parameters, variables, constants, classes, and types.

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 for a list of them. The standard does not specify a limit to the length of an identifier, but certain implementations of C++ only examine the first 31 characters to distinguish between identifiers.

A literal is a constant value that appears somewhere in a program. Since every value has a type, every literal has a type also. It is possible to have literals of each of the native data types, and also character string literals. Table 1.1 shows some examples of literals and their types.

String literals are special in C++, due to its historical roots in the C language. Example 1.14 shows how certain characters need to be escaped inside double-quoted string delimiters.

#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;
}

We compile and run the way we described earlier:

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"

Notice that this program shows a way to avoid very long lines when dealing with string literals. They can be broken at any white space character and are concatenated automatically using this syntax.