Every computer has a word size, indicating the nominal size of pointer data.
Since a virtual address is encoded by such as word, the most important system parameter determined by the word size is the maximum size of the virtual address space. For example, for a machine with w-bit word size, the virtual address can range from 0 to
The C language supports multiple data formats for both integer and floating-point data. And following chart shows the number of bytes typically allocated for different C data types.
| Signed | Unsigned | 32-bit | 64-bit |
|---|---|---|---|
| [signed] char | unsigned char | 1 | 1 |
| short | unsigned short | 2 | 2 |
| int | unsigned int | 4 | 4 |
| long | unsigned long | 4 | 8 |
| int32_t | unit32_t | 4 | 4 |
| int64_t | unit64_t | 8 | 8 |
| char* | - | 4 | 8 |
| float | - | 4 | 4 |
| double | - | 8 | 8 |
Most of the data type encode signed values, unless prefixed by the keyword unsigned or using the specific unsigned declaration for fixed-size data types. The exception to this is data type char: in many contexts, the program's behavior is insensitive to whether data type char is signed or unsigned.
And the chart also shows that a pointer uses the full word size of the program.
A string in C is encoded by an array of characters terminated by the null(having value 0) character. Each character is represented by some standard encoding, with the most common being the ASCII character code.
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