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| <h3 class="section">20.1 Integers</h3> |
| |
| <p><a name="index-integer-2320"></a> |
| The C language defines several integer data types: integer, short integer, |
| long integer, and character, all in both signed and unsigned varieties. |
| The GNU C compiler extends the language to contain long long integers |
| as well. |
| <a name="index-signedness-2321"></a> |
| The C integer types were intended to allow code to be portable among |
| machines with different inherent data sizes (word sizes), so each type |
| may have different ranges on different machines. The problem with |
| this is that a program often needs to be written for a particular range |
| of integers, and sometimes must be written for a particular size of |
| storage, regardless of what machine the program runs on. |
| |
| <p>To address this problem, the GNU C library contains C type definitions |
| you can use to declare integers that meet your exact needs. Because the |
| GNU C library header files are customized to a specific machine, your |
| program source code doesn't have to be. |
| |
| <p>These <code>typedef</code>s are in <samp><span class="file">stdint.h</span></samp>. |
| <a name="index-stdint_002eh-2322"></a> |
| If you require that an integer be represented in exactly N bits, use one |
| of the following types, with the obvious mapping to bit size and signedness: |
| |
| <ul> |
| <li>int8_t |
| <li>int16_t |
| <li>int32_t |
| <li>int64_t |
| <li>uint8_t |
| <li>uint16_t |
| <li>uint32_t |
| <li>uint64_t |
| </ul> |
| |
| <p>If your C compiler and target machine do not allow integers of a certain |
| size, the corresponding above type does not exist. |
| |
| <p>If you don't need a specific storage size, but want the smallest data |
| structure with <em>at least</em> N bits, use one of these: |
| |
| <ul> |
| <li>int_least8_t |
| <li>int_least16_t |
| <li>int_least32_t |
| <li>int_least64_t |
| <li>uint_least8_t |
| <li>uint_least16_t |
| <li>uint_least32_t |
| <li>uint_least64_t |
| </ul> |
| |
| <p>If you don't need a specific storage size, but want the data structure |
| that allows the fastest access while having at least N bits (and |
| among data structures with the same access speed, the smallest one), use |
| one of these: |
| |
| <ul> |
| <li>int_fast8_t |
| <li>int_fast16_t |
| <li>int_fast32_t |
| <li>int_fast64_t |
| <li>uint_fast8_t |
| <li>uint_fast16_t |
| <li>uint_fast32_t |
| <li>uint_fast64_t |
| </ul> |
| |
| <p>If you want an integer with the widest range possible on the platform on |
| which it is being used, use one of the following. If you use these, |
| you should write code that takes into account the variable size and range |
| of the integer. |
| |
| <ul> |
| <li>intmax_t |
| <li>uintmax_t |
| </ul> |
| |
| <p>The GNU C library also provides macros that tell you the maximum and |
| minimum possible values for each integer data type. The macro names |
| follow these examples: <code>INT32_MAX</code>, <code>UINT8_MAX</code>, |
| <code>INT_FAST32_MIN</code>, <code>INT_LEAST64_MIN</code>, <code>UINTMAX_MAX</code>, |
| <code>INTMAX_MAX</code>, <code>INTMAX_MIN</code>. Note that there are no macros for |
| unsigned integer minima. These are always zero. |
| <a name="index-maximum-possible-integer-2323"></a><a name="index-minimum-possible-integer-2324"></a> |
| There are similar macros for use with C's built in integer types which |
| should come with your C compiler. These are described in <a href="Data-Type-Measurements.html#Data-Type-Measurements">Data Type Measurements</a>. |
| |
| <p>Don't forget you can use the C <code>sizeof</code> function with any of these |
| data types to get the number of bytes of storage each uses. |
| |
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