Character processing function \x0d\ This category function is used to process a single character, including character category test and character case conversion \x0d\x0d\ header file ctype.h \x0d\ \ function list \x0d\ function category function instruction \ x0d \ Whether the character test is letters and numbers isalpha \x0d\X0d\. Whether to display the character isdigit \x0d\ isgraph \x0d\ whether to display the character isprint \x0d\ whether it is neither a space nor a function that can display the character is letters and numbers \x0d \ whether it is a space \ x0d. The uppercase letter is upper \ x0d \ 16 hexadecimal digit (0-9, A-F) character isxdigit \ x0d \ character case conversion function is converted to uppercase letter toupper \x0d\ lowercase letter to lower \ x0d \ \ registration \ x0d \. \x0d\\x0d\ header file local.h \x0d\ \ function list \x0d\ function category function usage description \x0d\ area control area setting setlocale \x0d\ number format convention query country's currency, date, time and other format conversion localeconv \ x0d \ \ x0d. This classification gives various mathematical calculation functions. It must be reminded that the data format in the ANSI C standard does not conform to the IEEE754 standard, but some C language compilers follow the IEEE754 (for example, Frinklin C5 1) \x0d\x0d\ header file math.h \x0d\\x0d\ \ function list \ x0d \ function category function usage details. X0d\ Error Condition Handling Domain Error (the input parameter value of the function is not within the specified range) \x0d\ Range Error (the return value of the function is not within the specified range) \x0d\ trigonometric function arccosine acos \x0d\ arcsine sin \x0d\ arctangent atan \x0d\ arctangent 2 atan2 \x0d\ cosine. X0d\ tangent tan \x0d\ hyperbolic function hyperbolic cosine cosh \x0d\ hyperbolic sine sinh \x0d\ hyperbolic tangent tanh \x0d\ exponential function exp \x0d\ exponential decomposition function frexp \x0d\ product exponential function fdexp \x0d\ natural logarithm log \x0d\ logarithm. Floating-point decomposition function modf \x0d\ power function pow \x0d\ square root function sqrt \x0d\ integer truncation, lower limit of absolute value and header file setjmp.h \x0d\x0d\ function list \ x0d \ function category function usage description \ x0d \ Save the calling environment setjmp \x0d\ Signal processing \x0d\ This classification function is used to handle those exceptions that occur during program execution. \x0d\x0d\ header file signal.h \x0d\\x0d\ \ function list \ x0d \ function usage description \ x0d \ Specify signal processing function signal \ x0d \ send signal raise \ x0d. \x0d\\x0d\ header file stdarg.h \x0d\ \ function list \x0d\ function category function usage details \x0d\ variable parameter access macro variable parameter start macro va_start \x0d\ variable parameter end macro va_end \x0d\ variable parameter access macro accesses the next variable parameter macro. I/O functions \x0d\ This classification is used to handle various I/O devices, including files and consoles, and various functions are realized in a \x0d\x0d\ header file stdio.h \x0d\ \x0d\ function list \x0d\ function usage details \ x0d \ file. Get the temporary file path tmpnam \x0d\ file access closed file fclose \x0d\ refresh buffer flush \ x0d \ open file fopen \x0d\ match the existing stream pointer with the new file freopen \ x0d \ set disk buff setbuf \ x0d \ Set disk buf setvbuf \ X0d \ Format input-output function Format output fprintf \ x0d \ Format output (console) printf \ x0d \ Format input (console) scan \ x0d \ Format output to buffer sprintf \ x0d \ Inputsscanf \ x0d \ Printformatvfprintf \ x0d \ Printformatf \ x0d \ Printformat string input fgets \x0d\ Character output fputc \x0d\ string output fputs \x0d\ character input (console) getc \x0d\ character input (console) getchar \x0d\ character input (console) gets \x0d\ character output (console) putc \x0d\ character output (console) putchar \ Character output (console) Character output to stream header ungetc \x0d\ direct input output direct stream reading operation fread \x0d\ direct stream writing operation fwrite \x0d\ file location file location moving fseek \x0d\ file location setting fsetpos \x0d\ get file location ftell \x0d\ file location reset zero reminder \ Error handling function error clearing clearerr \x0d\ file end judgment feof \x0d\ file error detection ferror \x0d\ get error prompt string perror \ x0d \ utility function \ x0d \ This classification gives some functions that cannot be classified according to the above, but are necessary for programming. \x0d\\x0d\ header file stdlib.h \x0d\ \ function list \x0d\ function category function usage details \x0d\ string conversion function string conversion to integer atoi \x0d\ string conversion to long integer atol \x0d\ string conversion to floating-point number strtod \x0d\ string conversion to long integer. Convert a string into an unsigned long integer Stroul \ x0d \ Set the initial value of a random function by the pseudo-random sequence generation function rand \x0d\ Storage management function allocates memory calloc \x0d\ Releases memory free \x0d\ Memory allocation malloc \x0d\ realloc \x0d\ The environment communication termination program abort \x0d\ exits the program execution, and clears the environment variable atexit \x0d\ exits the program execution \x0d\ reads the environment parameter getenv \x0d\ program pause, and temporarily executes another program system \x0d\ method of bisection (data must be sorted) bsearch \x0d\ quick sorting qsort \x0d\. Integer operation function abs \x0d\div \x0d\ Find the base quotient and remainder of division operation \x0d\ Find the base absolute value abs \ x0d \ Find the quotient and remainder ldiv \x0d\ Find the length shaping division. The multibyte character function obtains the number of bytes of multibyte characters mblen \x0d\ obtains the number of bytes of multibyte characters mbtowc \x0d\ multibyte character conversion wctomb \x0d\ multibyte string operation converts multibyte strings into integer arrays mbstowcs \x0d\ converts multibyte strings into character arrays mcstowbs \x0d\ \ String processing \ x0d \ Functions in this category are used to merge and compare strings \x0d\x0d\ header file string.h \ x0d \ \ function list \ x0d \ Detailed description of functions Block copy (target and source storage can overlap) memmove \ X0d \ String copy strcpy \ X0d \ stringcopystrcpy \ x0d \ stringconnection function stringconnection strcat \ x0d \ stringcomparison block comparison memcmp \ x0d \ String comparison strcmp \ x0d \ string (for non-English characters) strcol \ x0d \ String comparison by length strncmp \ x0d \ String conversion strxfrm \ x0d \ Character search memchr \ x0d \ Character search strrr \ x0d \ String search string lookup strpn \x0d\ String lookup strtr \ x0d \ String decomposition strtok \x0d\ Miscellaneous function string setting memset \ X0d\ Error string mapping strerror \x0d\ Find string length strlen \ x0d \ \ Date and time function \ x0d \ This category gives time and date processing function \x0d\x0d\ header file time.h \ x0d \ \ function list \ x0d \ function category function usage description \ Time operation function obtains processor clock \x0d\ obtains time difference \ x0d x0d \ gettime \x0d\ Time conversion function obtains time in ASCII code \ x0d \ obtains time in string form \ x0d \ obtains time in specified format \ strftime \ x0d \ \ Future development direction of function library \ x0d. \x0d\\x0d\ serial number library category header description \x0d\ 1 error handling errno.h \x0d\2 character processing ctype.h \x0d\3 localization local.h \x0d\4 mathematical function math.h \x0d\5 signal processing signal.h