在C語言中有6種基本數據類型：short、int、long、float、double、char
1）整型：short int、int、long int
2）浮點型：float、double
3）字符類型：char
因此，uint8_t / uint16_t / uint32_t /uint64_t這些數據類型都只是別名。這些數據類型中都帶有_t, _t 表示這些數據類型是通過typedef定義的，而不是新的數據類型。
那麼_t的意思到底表示什麼？它就是一個結構的標註，可以理解爲type/typedef的縮寫，表示它是通過typedef定義的。
一般來說，一個C的工程中一定要做一些這方面的工作，因爲你會涉及到跨平臺，不同的平臺會有不同的字長，所以利用預編譯和typedef可以讓你最有效的維護你的代碼。爲了用戶的方便，C99標準的C語言硬件爲我們定義了這些類型，我們放心使用就可以了。 按照posix標準，一般整形對應的*_t類型爲： 1字節 uint8_t 2字節 uint16_t 4字節 uint32_t 8字節 uint64_t
typedef signed char int8_t; typedef signed short int int16_t; typedef signed int int32_t; typedef signed __INT64 int64_t; /* exact-width unsigned integer types */ typedef unsigned char uint8_t; typedef unsigned short int uint16_t; typedef unsigned int uint32_t; typedef unsigned __INT64 uint64_t; /* 7.18.1.2 */ /* smallest type of at least n bits */ /* minimum-width signed integer types */ typedef signed char int_least8_t; typedef signed short int int_least16_t; typedef signed int int_least32_t; typedef signed __INT64 int_least64_t; /* minimum-width unsigned integer types */ typedef unsigned char uint_least8_t; typedef unsigned short int uint_least16_t; typedef unsigned int uint_least32_t; typedef unsigned __INT64 uint_least64_t; /* 7.18.1.3 */ /* fastest minimum-width signed integer types */ typedef signed int int_fast8_t; typedef signed int int_fast16_t; typedef signed int int_fast32_t; typedef signed __INT64 int_fast64_t; /* fastest minimum-width unsigned integer types */ typedef unsigned int uint_fast8_t; typedef unsigned int uint_fast16_t; typedef unsigned int uint_fast32_t; typedef unsigned __INT64 uint_fast64_t; /* 7.18.1.4 integer types capable of holding object pointers */ #if __sizeof_ptr == 8 typedef signed __INT64 intptr_t; typedef unsigned __INT64 uintptr_t; #else typedef signed int intptr_t; typedef unsigned int uintptr_t; #endif /* 7.18.1.5 greatest-width integer types */ typedef signed __LONGLONG intmax_t; typedef unsigned __LONGLONG uintmax_t;
注意：
typedef unsigned char uint8_t;
必須小心 uint8_t 類型變量的輸出。uint8_t類型變量轉化爲字符串時得到的會是ASCII碼對應的字符, 字符串轉化爲 uint8_t 變量時, 會將字符串的第一個字符賦值給變量.
uint8_t fieldID = 67; cerr<< "field=" << fieldID <<endl;
field=C
uint8_t fieldID = 67; cerr<< "field=" << (uint16_t) fieldID <<endl;
結果是：field=67