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Glibc:Functions

lastmod 2021-11-05created 2021-11-052 edits

List of GNU C functions.

Data conversion functions

  • strtof(): Converts a real-number string to a float
  • strtod(): Converts a real-number string to a double
  • strtoul(): Converts an integer string to an unsigned long integer in a chosen base
  • strtol(): Converts an integer string to an integer in a chosen base
  • atof(): Converts a decimal real-number string to a double
  • atol(): Converts a decimal integer string to a long integer
  • atoi(): Converts a decimal integer string to an integer

Working with files and directories

  • dup2(): Makes a copy of a file descriptor
  • dup(): Makes a copy of a file descriptor
  • ftruncate(): Changes a file to the specified size
  • truncate(): Changes a file to the specified size
  • fdopen(): Gets a stream pointer from a descriptor
  • lseek(): Moves the read/write pointer to an arbitrary position in a file
  • read(): Reads a file
  • fcntl(): Record locking
  • access(): Checks whether a file exists or its access permissions.
  • fsync(): Writes buffer contents to disk
  • sync(): Writes buffer contents to disk
  • chroot(): Sets the root directory]
  • fchown(): Changes ownership
  • chown(): Changes ownership
  • fchmod(): Changes a file's access permissions
  • chmod(): Changes file access permissions
  • rename(): Renames a file or directory
  • remove(): Deletes a file or directory
  • symlink(): Creates a symbolic link
  • unlink(): Deletes a link
  • link(): Creates a link
  • rewinddir(): Resets the directory read position to the beginning
  • readdir(): Gets an entry in a directory
  • closedir(): Closes a directory
  • opendir(): Opens a directory
  • getcwd(): Gets the current working directory
  • creat(): Creates a file
  • write(): Writes a file
  • close(): Closes a file
  • open(): Opens a file

I/O functions

  • fseek(): Moves the read/write position in a file
  • rewind(): Resets the file read/write position to the beginning
  • ftell(): Gets the read/write position in a file
  • I/O(): function clearerr Resets file error information
  • ferror(): Checks whether a file error occurred
  • feof(): Checks for end of file
  • ungetc(): Gives back the last character read
  • fwrite(): Writes buffer contents to a file
  • fread(): Reads the specified number of items from a file
  • fprintf(): Formatted output to a file
  • fscanf(): Reads formatted data from a file
  • fputs(): Writes a string to a file
  • fgets(): Reads a string from a file
  • fputc(): Writes a character to a file
  • fgetc(): Reads one character from a file
  • fclose(): Closes a file
  • fopen(): Opens a file
  • sprintf(): Formatted output to a memory area
  • sscanf(): Reads formatted data from a data area
  • printf(): Formatted output to the standard output device
  • scanf(): Reads formatted input from the standard input device
  • puts(): Writes a string to standard output
  • gets(): Reads a string from the standard device
  • putchar(): Writes a character to the standard output device
  • getchar(): Reads one character from the standard input device

IPC functions

  • semop(): Changes a semaphore value
  • semctl(): Controls a semaphore
  • semget(): Creates and accesses a semaphore
  • shmctl(): Checks/changes/removes shared memory information
  • shmdt(): Detaches shared memory from a process
  • shmat(): Attaches shared memory to a process
  • shmget(): Creates shared memory
  • msgctl(): Message queue status info/change/delete
  • msgrcv(): Receives data from a message queue
  • msgsnd(): Sends data to a message queue
  • msgget(): Creates a message queue
  • mkfifo(): Makes a FIFO pipe
  • pipe(): IPC using a pipe
  • pclose(): Closes a pipe
  • popen(): Creates a pipe

Math functions

  • log10(): Gets the common logarithm
  • log(): Gets the natural logarithm
  • exp(): Gets e to the power of x
  • tan(): Gets the tan value
  • cos(): Gets the cos value
  • sin(): Gets the sin value
  • sqrt(): Gets the square root
  • pow(): Gets the power
  • srand(): Sets the random number seed
  • rand(): Generates a random number
  • modf(): Gets the integer and fractional parts of a double value
  • floor(): Rounds down everything after the decimal point
  • ceil(): Rounds up everything after the decimal point
  • fmod(): Gets the remainder of a double division
  • ldiv(): Gets the quotient and remainder of a long integer division
  • div(): Gets the quotient and remainder of an int integer division
  • fabs(): Gets the absolute value of a double variable
  • labs(): Gets the absolute value of a long variable
  • abs(): Gets the absolute value of an int variable

Memory management functions

  • memset(): Initializes memory to a specific value
  • memcmp(): Compares the contents of two memory variables
  • memchr(): Searches memory for a character
  • memmove(): Copies a memory area, works on overlapping areas too
  • memcpy(): Copies a memory area
  • realloc(): Changes the size of dynamic memory
  • free(): Returns allocated memory
  • calloc(): Dynamic memory allocation with a specified element size
  • malloc(): Dynamic memory allocation

Search and sort functions

  • qsort(): Quicksort
  • hdestroy(): Deletes a hash table
  • hsearch(): Searches a hash table for data
  • hcreate(): Creates a hash table
  • twalk(): Visits the contents of every node in a binary tree
  • tdelete(): Deletes a node from a binary tree
  • tfind(): Binary tree search
  • tsearch(): Binary tree search and insert
  • bsearch(): Binary search
  • lfind(): Searches a table for data
  • lsearch(): Searches a table for data and adds it

Program execution functions

  • getopt_long(): Uses long-name options at runtime
  • unsetenv(): Deletes an environment variable
  • setenv(): Adds or modifies an environment variable
  • putenv(): Adds or modifies an environment variable
  • getenv(): Gets the value of an individual environment variable
  • environ(): Global variable holding the program's execution environment values
  • envp(): Argument of main that holds the program environment
  • getopt(): Gets program argument information
  • abort(): Forcibly terminates the program
  • assert(): Checks a given condition
  • perror(): Prints the error message
  • strerror(): Gets the error message for errno.
  • errno(): Gets the error number

Processor functions

  • getgrnam(): Gets group information by group name
  • getgrgid(): Gets group information by group ID
  • endgrent(): Closes the group file
  • setgrent(): Moves the group file read position to the top line
  • getgrent(): Reads the contents of the group file
  • endpwent(): Closes the password file
  • setpwent(): Moves the read position in the password file to the first line
  • getpwent(): Gets user information from the password file
  • getpwnam(): Gets user information by login user name
  • getpwuid(): Gets user information by user ID
  • getlogin(): Gets the logged-in user name
  • getegid(): Gets the effective group ID
  • getgid(): Gets the real group ID
  • geteuid(): Gets the effective user ID.
  • getuid(): Gets the real user ID.

Signal functions

  • sigsuspend(): Sets a signal block and waits
  • sigpending(): Checks blocked signals
  • sigpromask(): Sets signals to the pending state
  • alarm(): Sends SIGALRM at the specified time
  • raise(): Sends a signal to the process itself
  • pause(): Waits until a signal is received
  • kill(): Sends a signal
  • sigaction(): Versatile signal handling
  • signal(): Sets how a signal is handled
  • sleep(): Waits for the specified time
  • sigfillset(): Adds all signals to a signal set
  • sigismember(): Checks whether a signal is in a signal set
  • sigdelset(): Removes a signal from a signal set
  • sigaddset(): Adds a signal to a signal set

Socket functions

  • gethostbyname(): Gets hostent information from a domain name
  • gethostname(): Gets the host name
  • recvfrom(): Receives data from a socket
  • sendto(): Sends data through a socket
  • recv(): Receives data from a socket
  • send(): Sends data through a socket
  • accept(): Accepts a client connection request
  • connect(): Requests a connection to a server
  • listen(): Waits until a client connection request arrives
  • inet_addr(): Gets a long numeric IP address from an IP string
  • ntohl(): long network byte order to host byte order
  • ntohs(): short network byte order to host byte order
  • htnol(): Host byte order to network byte order
  • htnos(): Host byte order to network byte order
  • bind(): Assigns an IP address and port number to a socket
  • socket(): Creates a socket

Date and time functions

  • clock(): Gets the time elapsed since the program started
  • difftime(): Gets the difference between dates and times
  • strftime(): Gets a date and time string
  • mktime(): Gets an integer date and time value from a specified date and time
  • gmtime(): Gets Coordinated Universal Time information from a time_t value
  • localtime(): Gets local time information from a time_t value
  • ctime(): Converts a time in seconds to a readable string
  • time(): Gets the current time value

String handling functions

  • isdigit(): Checks whether a character is a digit ('0'~'9')
  • iscntrl(): Checks whether a character is a control character
  • isblank(): Checks whether it is a space or tab character
  • isascii(): Checks whether a character is an ASCII character
  • isalpha(): Checks whether it is an alphabetic character
  • isalnum(): Checks whether it is an alphabetic character or a digit
  • strncmp(): Compares strings up to a length
  • strcmp(): Compares strings
  • strncat(): Concatenates two strings with a specified length
  • strcat(): Concatenates two strings
  • sigemptyset(): Clears all contents of a signal set
  • strtok(): Splits a string by characters
  • strpbrk(): Gets a pointer to where any of the specified characters first appears in a string
  • strcspn(): Gets the length of the part of a string not containing the specified characters
  • strspn(): Gets the length of the part of a string made up of the specified characters
  • strstr(): Searches a string for the position of a given substring
  • strrchr(): Searches for the position of a given character from the end of a string
  • strchr(): Searches a string for the position of a given character
  • strlen(): Gets the length of a string
  • strdup(): Makes a clone of a string
  • strncpy(): Copies the specified number of characters of a string
  • strcpy(): Copies a string
  • strncasecmp(): Compares strings up to the specified length, ignoring case
  • strcasecmp(): Compares strings ignoring case
  • tolower(): Converts an uppercase letter to lowercase and returns it
  • toupper(): Converts a lowercase letter to uppercase
  • isxdigit(): Checks whether a character is a hexadecimal digit
  • isupper(): Checks whether a character is uppercase
  • isspace(): Checks whether a character is a whitespace character
  • ispunct(): Checks whether a character is a punctuation character
  • isprint(): Checks whether a character is printable
  • islower(): Checks whether a character is lowercase
  • isgraph(): Checks whether a character is printable

User and group management functions

  • getgrnam(): Gets group information by group name
  • getgrgid(): Gets group information by group ID
  • endgrent(): Closes the group file
  • setgrent(): Moves the group file read position to the top line
  • getgrent(): Reads the contents of the group file
  • endpwent(): Closes the password file
  • setpwent(): Moves the read position in the password file to the first line
  • getpwent(): Gets user information from the password file
  • getpwnam(): Gets user information by login user name
  • getpwuid(): Gets user information by user ID
  • getlogin(): Gets the logged-in user name
  • getegid(): Gets the effective group ID
  • getgid(): Gets the real group ID
  • geteuid(): Gets the effective user ID.
  • getuid(): Gets the real user ID.

See also

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