The Standard C Library

One of the reasons C is a popular language is that it is a "high level" "low level" 

language. It provides high level programming constructs such as functions, loop, and test which make it easy 

to write modular, well structured code. 

At the same time, it provides low level operators and freedom to allow a programer to create their own tools 

for manipulating their data. 

Up until now, we have largely written our own tools when we needed them (e.g. chrutil.h). However, the standard C library provides a large number of built-in utility functions and macros we can use instead of writing our own. The full standard C library is documented in Appendix C of the textbook. The functions provided fall into several categories:

 Character Class Tests

Character class tests:

• isalnum
• alpha numeric (letter, digit)
• isalpha
• alpha (letter)
• iscntrl
• control
• isdigit
• digit
• isgraph
• graphic (printable except for space)
• islower
• lower case letter
• isprint
• printable
• ispunct
• punctuation
• isspace
• white space
• isupper
• upper case letter
• isxdigit
• hexadecimal digit

Character Conversions:

• tolower
• lower case
• toupper
• upper case

 String Functions

String Functions:

• strcpy
• copies a string to another
• strncpy
• copies n characters from a string to another
• strcat
• concatenates two strings
• strncat
• concatenates n characters from a string onto another
• strcmp
• compares two strings
• strncmp
• compares n characters of two strings
• strchr
• returns the first occurrence of character in a string
• strrchr
• returns the last occurrence of character in a string
• strspn
• returns the length of leading characters in a string that are contained in a specified string
• strcspn
• returns the length of leading characters in a string not contained in a specified string
• strpbrk
• returns first occurrence in a string of any character in another string
• strstr
• returns the first occurrence of one string in another
• strlen
• returns length of a string
• strerror
• returns a string corresponding to an error number
• strtok
• returns a token from a string delimited by specified characters

Memory Functions (Memory treated as an array):

• memcpy
• copies n characters from one address to another
• memmove
• same as memcpy, except that overlap is allowed
• memcmp
• compares n characters at specified addresses
• memchr
• returns first occurrence of a character in a string at an address
• memset
• stores a character in first n positions starting at specified address
• 
  

 Utility Functions including system().

The system() function is just a convenient way to execute a command from within a C program. The prototype is:

     int system(char *s);

In Unix, the string, s, is given to a shell to run. When the command completes, system() returns.

For example, one way I implemented the startup screen in the miensfeld game was to use:

        system("cat title1");

Conversions:

• atof
• converts a string to a float
• atoi
• converts a string to an integer
• atol
• converts a string to a long
• strtod
• converts a string to double
• strtol
• converts a string to long
• strtoul
• converts a string to unsigned long

Pseudo-random generator:

• rand
• generates a random integer
• srand
• seeds the random generator

Dynamic memory allocation:

• calloc
• dynamically allocates memory for n items of size
• malloc
• dynamically allocates memory for n bytes
• realloc
• reallocates a block of memory with a different size
• free
• frees previously allocated memory

Program Termination:

• abort
• abnormally terminates a program
• exit
• normally terminates a program

System Interface:

• system
• executes system commands

Search and Sort:

• bsearch
• binary search function
• qsort
• sort function

Other Utility:

• abs
• returns absolute value of an integer
• labs
• returns absolute value of a long
• div
• int type: returns quotient and remainder of x / y
• ldiv
• long type: similar to div

 Math Functions

NOTE: to use the math library, you must include <math.h> AND link the math library on the cc line:

               cc whatever.c -o whatever -lm

Trigonometric:

• sin
• sine
• cos
• cosine
• tan
• tangent
• asin
• arc sine
• acos
• arc cosine
• atan
• arc tangent, range first quadrant
• atan2
• arc tangent, range two quadrants

Hyperbolic:

• sinh
• hyperbolic sine
• cosh
• hyperbolic cosine
• tanh
• hyperbolic tangent

Logarithmic:

• exp
• exponential
• log
• natural logarithm
• log10
• base 10 logarithm

Power and Square-Root:

• pow
• yth power of x
• sqrt
• square root

Rounding:

• ceil
• smallest whole number greater than x
• floor
• largest whole number less than x

Others:

• fabs
• absolute value of a floating point
• ldexp
• generates a base 2 fraction times an exponent
• frexp
• splits a number into a base 2 fraction and an exponent
• modf
• splits a number into fractional and integral parts
• fmod
• floating point remainder of x / y, x and y are double

 File I/O Functions

File open and close:

• fopen
• opens a file stream
• freopen
• open a file and associate with a stream
• fflush
• flushes an output file stream buffer
• fclose
• closes a file stream

File management:

• remove
• removes a named file
• rename
• renames an old file name to a new name
• tmpfile
• creates a temporary file
• setbuf
• sets a file stream as buffered or unbuffered

Formatted I/O:

• fprintf
• writes to a file
• printf
• writes to standard output
• sprintf
• writes to a string
• fscanf
• reads from a file
• scanf
• reads from standard input
• sscanf
• reads from a string

Character and String I/O:

• fgetc
• reads a character from a file
• fgets
• reads a string from a file
• fputc
• writes a character to a file
• fputs
• writes a string to a file
• getc
• reads a character from a file
• getchar
• reads a character from standard input
• gets
• reads a string from standard input
• putc
• writes a character to a file
• putchar
• writes a character to standard output
• puts
• writes a string to standard output
• ungetc
• puts a character back onto a stream; only one character per stream may be allowed to be put back

Block I/O:

• fread
• reads a block from a file
• fwrite
• writes a block to a file

File Pointer Positioning:

• fseek
• seeks a position in a file stream
• ftell
• returns a position in a stream
• rewind
• essentially reopens a file
• fgetpos
• gets current position in a stream
• fsetpos
• sets the current position in a stream

File Error Handling:

• clearerr
• clears error and end of file indicators
• feof
• chaecks end of file indicator
• ferror
• checks file error indicator
• perror
• prints a specified string and an error message for errno

 Limit Macros

Many implementation dependent sizes are defined in these files. The following are examples of some of them. The values specified are mimimum values; larger values are acceptable.

 Others

Thre are several other library functions and header files of limited use that we have not included here. Readers should refer to appropriate manuals. Some of the categories are:

Error Numbers <errno.h>

Declares integer type errno which will contain the number of an error when it occurs.

Signals <signal.h>

Provides facilities to handle exceptional situations such as interrupts or errors.

Date and Time Functions <time.h>

Provides clock functions as well as date and time functions.

Variable Argument Lists <stdarg.h>

Provides failities to step through a list of function arguments of unknown number and type.

Non-local Jumps <setjmp.h>

Provides a way of avoiding normal function calls and returns.

A full alphabetic listing of the C library is also found in the Appendix of your Textbook.

C library functions are also documented on-line, for example here (you just have to put up with the ads).