ANSI C Back to MrGibson.com
ANSI C in the 1980s C was originally developed at Bell Labs to construct utilities running on Unix. It was applied to re-implementing the kernel of the Unix operating system. During the 1980s, C gradually gained popularity. By 1986 and 1987, the C language was a star topic among the geeks. One of the reasons that C became popular is that C could be used as a form of "high level assembly language", without a compiler having to know or care about what that effect might be. The ANSI standard was completed in 1989 and ratified as "Programming Language C." Note: This document is a work in progress.
Headers Headers can be added at the beginning of the code for the functions needed. #include <stdio.h> #include <stdlib.h> #include <string.h> #include <ctype.h> #include <math.h> <stdio.h> contains function prototypes, macros, and type definitions for standard input and output functions, including:
fclose() Closes a file Example: if (fclose(file) == EOF) { printf("Error closing file"); return 1; }
feof() Returns a true value when the position indicator has reached the end of the file
ferror() Returns a true value if a recent file operation had an error
fgetc() Returns the ASCII value of a character in a file and advances the position indicator
fgets() Reads a line from a file and advances the position indicator
fopen() Opens a file and returns a file pointer for use in file handling functions
fprintf() Writes a formatted string into a file
fputc() Writes a character into a file and advances the position indicator
fputs() Writes a string into a file and advances the position indicator
fread() Reads data from a file and writes it into a block of memory
fscanf() Reads formatted data from a file and writes it into a number of memory locations
fseek() Moves the position indicator of a file pointer
ftell() Returns the value of the position indicator of a file pointer
fwrite() Writes data from a block of memory into a file
getc() The same as fgetc()
getchar() Reads one character of user input and returns its ASCII value
printf() Writes a formatted string to the console
putc() The same as fputc()
putchar() Outputs a single character to the console
puts() Outputs a string to the console
remove() Deletes a file
rename() Changes the name of a file
rewind() Moves the position indicator to the beginning of the file
scanf() Reads formatted data from user input and writes it into a number of memory locations
snprintf() Writes a formatted string into a char array (memory-safe)
sprintf() Writes a formatted string into a char array
sscanf() Reads a formatted string from a char array and writes it into a number of memory locations
NULL: Represents a null pointer.
EOF: Represents the end-of-file marker. Example: if (fclose(file) == EOF) { printf("Error closing file"); return 1; }
FILE: A structure type used to represent a file stream.
The <stdlib.h> header (standard library) provides a variety of commonly used functions.
abs() Return the absolute (positive) value of a whole number
atof() Return a double value from a string representation of a number
atoi() Return an int value from a string representation of a whole number
atol() Return a long int value from a string representation of a whole number
atoll() Return a long long int value from a string representation of a whole number
calloc() Allocate dynamic memory and fill it with zeroes
div() Return the quotient and remainder of an integer division
exit() End the program
free() Deallocate dynamic memory
malloc() Allocate dynamic memory
qsort() Sort the contents of an array
rand() Generate a random integer
realloc() Reallocate dynamic memory
srand() Initialize the random number generator
The <string.h> library has many functions that allow you to perform tasks on strings. A list of all string functions can be found in the table below:
memchr() Returns a pointer to the first occurrence of a value in a block of memory
memcmp() Compares two blocks of memory to determine which one represents a larger numeric value
memcpy() Copies data from one block of memory to another
memmove() Copies data from one block of memory to another accounting for the possibility that the blocks of memory overlap
memset() Sets all of the bytes in a block of memory to the same value
strcat() Appends one string to the end of another
strchr() Returns a pointer to the first occurrence of a character in a string
strcmp() Compares the ASCII values of characters in two strings to determine which string has a higher value
strcoll() Compares the locale-based values of characters in two strings to determine which string has a higher value
strcpy() Copies the characters of a string into the memory of another string
strcspn() Returns the length of a string up to the first occurrence of one of the specified characters
strerror() Returns a string describing the meaning of an error code
strlen() Return the length of a string
strncat() Appends a number of characters from a string to the end of another string
strncmp() Compares the ASCII values of a specified number of characters in two strings to determine which string has a higher value
strncpy() Copies a number of characters from one string into the memory of another string
strpbrk() Returns a pointer to the first position in a string which contains one of the specified characters
strrchr() Returns a pointer to the last occurrence of a character in a string
strspn() Returns the length of a string up to the first character which is not one of the specified characters
strstr() Returns a pointer to the first occurrence of a string in another string
strtok() Splits a string into pieces using delimiters
strxfrm() Convert characters in a string from ASCII encoding to the encoding of the current locale
The <ctype.h> header provides many functions for classifying and modifying characters.
isalnum() Checks whether a character is alphanumeric
isalpha() Checks whether a character is a letter
isblank() Checks whether a character is a space or tab
iscntrl() Checks whether a character is a control character
isdigit() Checks whether a character is a decimal digit
isgraph() Checks whether a character has a graphical representation
islower() Checks whether a character is a lowercase letter
isprint() Checks whether a character is a printable character
ispunct() Checks whether a character is a punctuation character
isspace() Checks whether a character is a whitespace character
isupper() Checks whether a character is an uppercase letter
isxdigit() Checks whether a character is a hexadecimal digit
tolower() Returns a lowercase version of a character
toupper() Returns an uppercase version of a character
The <math.h> library has many functions that allow you to perform mathematical tasks on numbers.
acos(x) Returns the arccosine of x, in radians
acosh(x) Returns the hyperbolic arccosine of x
asin(x) Returns the arcsine of x, in radians
asinh(x) Returns the hyperbolic arcsine of x
atan(x) Returns the arctangent of x as a numeric value between -PI/2 and PI/2 radians
atan2(y, x) Returns the angle theta from the conversion of rectangular coordinates (x, y) to polar coordinates (r, theta)
atanh(x) Returns the hyperbolic arctangent of x
cbrt(x) Returns the cube root of x
ceil(x) Returns the value of x rounded up to its nearest integer
copysign(x, y) Returns the first floating point x with the sign of the second floating point y
cos(x) Returns the cosine of x (x is in radians)
cosh(x) Returns the hyperbolic cosine of x
exp(x) Returns the value of Ex
exp2(x) Returns the value of 2x
expm1(x) Returns ex-1
erf(x) Returns the value of the error function at x
erfc(x) Returns the value of the complementary error function at x
fabs(x) Returns the absolute value of x
fdim(x) Returns the positive difference between x and y
floor(x) Returns the value of x rounded down to its nearest integer
fma(x, y, z) Returns x*y+z without losing precision
fmax(x, y) Returns the highest value of a floating x and y
fmin(x, y) Returns the lowest value of a floating x and y
fmod(x, y) Returns the floating point remainder of x/y
frexp(x, y) With x expressed as m*2n, returns the value of m (a value between 0.5 and 1.0) and writes the value of n to the memory at the pointer y
hypot(x, y) Returns sqrt(x2 +y2) without intermediate overflow or underflow
ilogb(x) Returns the integer part of the floating-point base logarithm of x
ldexp(x, y) Returns x*2y
lgamma(x) Returns the logarithm of the absolute value of the gamma function at x
llrint(x) Rounds x to a nearby integer and returns the result as a long long integer
llround(x) Rounds x to the nearest integer and returns the result as a long long integer
log(x) Returns the natural logarithm of x
log10(x) Returns the base 10 logarithm of x
log1p(x) Returns the natural logarithm of x+1
log2(x) Returns the base 2 logarithm of the absolute value of x
logb(x) Returns the floating-point base logarithm of the absolute value of x
lrint(x) Rounds x to a nearby integer and returns the result as a long integer
lround(x) Rounds x to the nearest integer and returns the result as a long integer
modf(x, y) Returns the decimal part of x and writes the integer part to the memory at the pointer y
nan(s) Returns a NaN (Not a Number) value
nearbyint(x) Returns x rounded to a nearby integer
nextafter(x, y) Returns the closest floating point number to x in the direction of y
nexttoward(x, y) Returns the closest floating point number to x in the direction of y
pow(x, y) Returns the value of x to the power of y
remainder(x, y) Return the remainder of x/y rounded to the nearest integer
remquo(x, y, z) Calculates x/y rounded to the nearest integer, writes the result to the memory at the pointer z and returns the remainder.
rint(x) Returns x rounded to a nearby integer
round(x) Returns x rounded to the nearest integer
scalbln(x, y) Returns x*Ry (R is usually 2)
scalbn(x, y) Returns x*Ry (R is usually 2)
sin(x) Returns the sine of x (x is in radians)
sinh(x) Returns the hyperbolic sine of x
sqrt(x) Returns the square root of x
tan(x) Returns the tangent of x (x is in radians)
tanh(x) Returns the hyperbolic tangent of x
tgamma(x) Returns the value of the gamma function at x
trunc(x) Returns the integer part of x ----------- #define ----------- types: char int long void ----------- FILE fclose for if/then/else open printf rand sprintf srand switch