| Standard Library Header File | Explanation |
| assert.h | Contains macros and information for adding diagnostics that aid program debugging |
| ctype.h | Contains function prototypes for functions that test characters for certain properties, and function prototypes that can be used to convert lowercase to uppercase and vice versa. |
| errno.h | Defines macros that are useful for reporting error conditions. |
| float.h | Contains the floating point size limits of the system. |
| limits.h | Contains the integral size limits of the system. |
| locale.h | Contains function prototypes and other information that enables a program to be modified for the current locale on which it is running. |
| math.h | Contains function prototypes for the math library functions. |
| setjmp.h | Contains function prototypes for functions that allow bypassing of the usual function call and return sequence. |
| signal.h | Contains function prototypes and macros to handle various conditions that may arise during program execution. |
| stdarg.h | Defines macros for dealing with a list of arguments to a function whose number and types are unknown. |
| stddef.h | Contains definitions of types used for performing certain calculations. |
| stdlib.h | Contains function prototypes for conversion of numbers to text and text to numbers, memory allocation, random numbers, and other utility functions. |
| string.h | Contains function prototypes for string processing functions. |
| time.h | Contains function prototypes and types for manipulating the time and date. |