1.13. C++ Simple Types

1.13. C++ Simple Types
	Chapter 1. C++ Introduction

[ fromfile: cppintro.xml id: simpletypes ]

The simple types supported in C/C++ are listed in Table 1.2.

C/C++ also provides a special symbol that signifies the absence of type information: void.

C++ simple types can (variously) be modified by the following keywords to produce other simple types.
- short
- long
- signed
- unsigned ^[8]

Table 1.2. Simple Types Hierarchy

byte/char Types	Integral Types	Floating Point Types
`bool`	`short int`	`float`
`char`	`unsigned short`	`double`
`signed char`	`int`	`long double`
`unsigned char`	`unsigned int`
`wchar_t`	`anyType*`
	`long int`
	`unsigned long`

You can also omit signed from most types because that is the default.

C++ Object Size

Object size in C++ is expressed in terms of the size of char.
the size of char is 1.
the ANSI/ISO standard for C++ does not specify the size of any of the types displayed in Table 1.2.
It guarantees only that a given type (e.g., int) must not be smaller than one that appears above it (e.g., short) in the table.

The operator sizeof() returns the number of char-sized memory cells (typically 8-bit bytes) needed to store the given expression.
Example 1.18 shows how sizeof() can be used and some of the values it returns on a 32-bit x86 system.
sizeof() can take arguments that are value expressions or type expressions.

Example 1.18. src/early-examples/size/qsize.cpp

#include <QString>
#include <QTextStream>
#include <QChar>
#include <QDate>

int main() {
    QTextStream cout(stdout);
    char array1[34] = "This is a dreaded C array of char";
    char array2[] = "if not for main, we could avoid it entirely.";
    char* charp = array1;                                       
    QString qstring = "This is a unicode QString. Much preferred." ;
    Q_ASSERT (sizeof(i) == sizeof(int));
    cout << "  c type sizes: \n";
    cout << "sizeof(char) = " << sizeof(char) << '\n';
    cout << "sizeof(wchar_t) = " << sizeof(wchar_t) << '\n';
    cout << "sizeof(int) = " << sizeof(int) << '\n';
    cout << "sizeof(long) = " << sizeof(long) << '\n';
    cout << "sizeof(float) = " << sizeof(float) << '\n';
    cout << "sizeof(double) = " << sizeof(double) << '\n';
    cout << "sizeof(double*) = " << sizeof(double*) << '\n';
    cout << "sizeof(array1) = " << sizeof(array1) << '\n';
    cout << "sizeof(array2) = " << sizeof(array2) << '\n';
    cout << "sizeof(char*) = " << sizeof(charp) << endl;
    cout << "  qt type sizes: \n";
    cout << "sizeof(QString) = " << sizeof(QString) << endl;
    cout << "sizeof(qint32) = " << sizeof (qint32) << "\n";     
    cout << "sizeof(qint64) = " << sizeof(qint64) << '\n';      
    cout << "sizeof(QChar) = " << sizeof (QChar) << endl;       
    cout << "sizeof(QDate) = " << sizeof(QDate) << endl; 
    cout << "qstring.length() = " << qstring.length() << endl;  
    return 0;
}
Output:
 
(example run on 32-bit system)
sizeof(char) = 1
sizeof(wchar_t) = 4
sizeof(int) = 4
sizeof(long) = 4
sizeof(float) = 4
sizeof(double) = 8
sizeof(double*) = 4
sizeof(array1) = 34
sizeof(array2) = 45
sizeof(char*) = 4
  qt type sizes:
sizeof(QString) = 4
sizeof(qint32) = 4
sizeof(qint64) = 8
sizeof(QChar) = 2
sizeof(QDate) = 4
qstring.length() = 42

	Pointer to first element of array.
	Guaranteed to be 32 bits on all platforms.
	Guaranteed to be 64 bits on all platforms.
	Twice as big as a char
	For # of bytes, be sure to take into account the size of `QChar`.

Notice that all pointers are the same size, regardless of their type.

Note the difference between sizeof(qstring) and qstring.length()

	Initialization of Basic-Typed Variables
	When a variable is of a basic type, it must be initialized! Uninitialized variables of basic types have undefined values on program startup. They may have initial value 0 when running in a debugger and have garbage values when run in other envrionments.

^[8] For further discussion of the differences between signed an unsigned integral types, see Section 19.5.


1.12.1. Exercises: Identifiers, Types, and Literals		1.13.1. `main`, and Command-Line Arguments