The library functions of the C language refer to some functions that have been packaged and can be called directly to complete some common tasks, including string processing, mathematical calculations, input and output, etc. The C language standard library is divided into two types: system header files and third-party header files.
The system header files refer to the standard library functions provided by the C language, which can be used directly in the program without additional installation or import of library files. Common system header files include stdio.h (standard input and output library), stdlib.h (standard library functions), string.h (string processing functions), etc. To use these functions, the corresponding header files need to be introduced into the program.
Third-party header files refer to library functions written and shared by other developers, which can be integrated into programs by importing corresponding library files or using package management tools to download and integrate them. Common third-party library functions include GMP (high-precision mathematical calculation library), OpenSSL (encryption library), libcurl (network programming library), etc.
The standard library functions of the C language are divided into multiple header files. Here are some commonly used header files and the functions they contain:
- stdio.h: Input and output processing related functions, such as printf, scanf, fgets, fopen, etc.
- string.h: Functions related to string operations, such as strcpy, strcat, strlen, strchr, etc.
- math.h: Functions related to mathematical calculations, such as sqrt, sin, cos, abs, etc.
- time.h: Time and date processing related functions, such as time, ctime, strftime, etc.
- stdlib.h: Commonly used function library functions, such as malloc, realloc, free, exit, etc.
- ctype.h: character type processing related functions, such as isalpha, isdigit, toupper, tolower, etc.
- assert.h: Program assertion related functions, such as assert, etc.
- errno.h: Error handling related functions, such as errno, perror, etc.
- signal.h: signal processing related functions, such as signal, raise, etc.
- stdarg.h: Variable parameter processing related functions, such as va_start, va_arg, va_end, etc.
A large number of functions and constants are defined in these header files, which can help us simplify the code development process.