Identifiers, Types, and Literals

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, as well as character string literals. Table 1.1 shows some examples of literals.

Table 1.1. Examples of Literals

Literal	Meaning
5	an int literal
5u	u or U specifies unsigned int
5L	l or L specifies long int after an integer
05	an octal int literal
0x5	a hexadecimal int literal
true	a bool literal
5.0F	f or F specifies single precision floating point literal
5.0	a double precision floating point literal
5.0L	l or L specifies long double if it comes after a floating point
'5'	a char literal (ASCII 53)
"50"	a const char* containing the chars '5', '0', and ''
"any" "body"	"anybody"
'a'	alert
'\'	backslash
''	backspace
' '	carriage return
'"	single quote
'"'	double quote
'f'	formfeed (newpage)
' '	tab
' '	newline char literal
" "	newline followed by null terminator (const char*)
''	null character
'v'	vertical tab
"a string with newline "	another const char*

String literals are special in C++, due to its historical roots in the C language. Example 1.6 shows how certain characters need to be escaped inside double-quoted string delimiters.

Example 1.6. src/early-examples/literals.cpp

#include 
#include 

int main() {
 using namespace std;
 const char* charstr = "this is one very long string "
 "so I will continue it on the next line";
 string str = charstr; <-- 1
 cout << str << endl;
 cout << "
A	b\c'd"" << endl;
 return 0;
}

 

(1)STL strings can hold onto C-style char* strings.

We compile and run the way we described earlier:

src/early-examples> g++ -ansi -pedantic -Wall literals.cpp
src/early-examples> ./a.out

The output should look something like this:

this is one very long string so I will continue it on the next line
A bc'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.

Exercises: Identifiers, Types, and Literals

Modify Example 1.6 so that, with a single output statement, the output becomes:

1.	GNU stands for "GNU's Not Unix".
2.	Title 1 "Cat Clothing" Title 2 "Dog Dancing"