标准C函数库和POSIX函数库的关系

The C POSIX library is a specification of a C standard library for POSIX systems. It was developed at the same time as the ANSI C standard. Some effort was made to make POSIX compatible with standard C; POSIX includes additional functions to those introduced in standard C.

一言以蔽之：POSIX库函数是C标准库函数的超集。

1 标准C库

<assert.h>      Contains the assert macro, used to assist with detecting logical errors and other types of bug in debugging versions of a program.
<complex.h> C99 A set of functions for manipulating complex numbers.
<ctype.h>       Defines set of functions used to classify characters by their types or to convert between upper and lower case in a way that is independent of the used character set (typically ASCII or one of its extensions, although implementations utilizing EBCDIC are also known).
<errno.h>       For testing error codes reported by library functions.
<fenv.h>    C99 Defines a set of functions for controlling floating-point environment.
<float.h>       Defines macro constants specifying the implementation-specific properties of the floating-point library.
<inttypes.h>    C99 Defines exact width integer types.
<iso646.h>  NA1 Defines several macros that implement alternative ways to express several standard tokens. For programming in ISO 646 variant character sets.
<limits.h>      Defines macro constants specifying the implementation-specific properties of the integer types.
<locale.h>      Defines localization functions.
<math.h>        Defines common mathematical functions.
<setjmp.h>      Declares the macros setjmp and longjmp, which are used