C Reference Card (ANSI)
Program Structure/Functions
type fnc(type1, . . . ); function prototype
type name; variable declaration
int main(void) { main routine
declarations local variable declarations
statements
}
type fnc(arg1, . . . ) { function definition
declarations local variable declarations
statements
return value;
}
/* */ comments
int main(int argc, char *argv[]) main with args
exit(arg); terminate execution
C Preprocessor
include library file #include
include user file #include "filename"
replacement text #define name text
replacement macro #define name(var) text
Example. #define max(A,B) ((A)>(B) ? (A) : (B))
undefine #undef name
quoted string in replace #
Example. #define msg(A) printf("%s = %d", #A, (A))
concatenate args and rescan ##
conditional execution #if, #else, #elif, #endif
is name defined, not defined? #ifdef, #ifndef
name defined? defined(name)
line continuation char \
Data Types/Declarations
character (1 byte) char
integer int
real number (single, double precision) float, double
short (16 bit integer) short
long (32 bit integer) long
double long (64 bit integer) long long
positive or negative signed
non-negative modulo 2m unsigned
pointer to int, float,. . . int*, float*,. . .
enumeration constant enum tag {name1=value1,. . . };
constant (read-only) value type const name;
declare external variable extern
internal to source file static
local persistent between calls static
no value void
structure struct tag {. . . };
create new name for data type typedef type name;
size of an object (type is size_t) sizeof object
size of a data type (type is size_t) sizeof(type)
Initialization
initialize variable type name=value;
initialize array type name[]={value1,. . . };
initialize char string char name[]="string";
c© 2007 Joseph H. Silverman Permissions on back. v2.2
Constants
suffix: long, unsigned, float 65536L, -1U, 3.0F
exponential form 4.2e1
prefix: octal, hexadecimal 0, 0x or 0X
Example. 031 is 25, 0x31 is 49 decimal
character constant (char, octal, hex) 'a', '\ooo', '\xhh'
newline, cr, tab, backspace \n, \r, \t, \b
special characters \\, \?, \', \"
string constant (ends with '\0') "abc. . . de"
Pointers, Arrays & Structures
declare pointer to type type *name;
declare function returning pointer to type type *f();
declare pointer to function returning type type (*pf)();
generic pointer type void *
null pointer constant NULL
object pointed to by pointer *pointer
address of object name &name
array name[dim]
multi-dim array name[dim1][dim2]. . .
Structures
struct tag { structure template
declarations declaration of members
};
create structure struct tag name
member of structure from template name.member
member of pointed-to structure pointer -> member
Example. (*p).x and p->x are the same
single object, multiple possible types union
bit field with b bits unsigned member: b;
Operators (grouped by precedence)
struct member operator name.member
struct member through pointer pointer->member
increment, decrement ++, --
plus, minus, logical not, bitwise not +, -, !, ~
indirection via pointer, address of object *pointer, &name
cast expression to type (type) expr
size of an object sizeof
multiply, divide, modulus (remainder) *, /, %
add, subtract +, -
left, right shift [bit ops] <<, >>
relational comparisons >, >=, <, <=
equality comparisons ==, !=
and [bit op] &
exclusive or [bit op] ^
or (inclusive) [bit op] |
logical and &&
logical or ||
conditional expression expr1 ? expr2 : expr3
assignment operators +=, -=, *=, . . .
expression evaluation separator ,
Unary operators, conditional expression and assignment oper-
ators group right to left; all others group left to right.
Flow of Control
statement terminator ;
block delimiters { }
exit from switch, while, do, for break;
next iteration of while, do, for continue;
go to goto label;
label label: statement
return value from function return expr
Flow Constructions
if statement if (expr1) statement1
else if (expr2) statement2
else statement3
while statement while (expr)
statement
for statement for (expr1; expr2; expr3)
statement
do statement do statement
while(expr);
switch statement switch (expr) {
case const1: statement1 break;
case const2: statement2 break;
default: statement
}
ANSI Standard Libraries
Character Class Tests
alphanumeric? isalnum(c)
alphabetic? isalpha(c)
control character? iscntrl(c)
decimal digit? isdigit(c)
printing character (not incl space)? isgraph(c)
lower case letter? islower(c)
printing character (incl space)? isprint(c)
printing char except space, letter, digit? ispunct(c)
space, formfeed, newline, cr, tab, vtab? isspace(c)
upper case letter? isupper(c)
hexadecimal digit? isxdigit(c)
convert to lower case tolower(c)
convert to upper case toupper(c)
String Operations
s is a string; cs, ct are constant strings
length of s strlen(s)
copy ct to s strcpy(s,ct)
concatenate ct after s strcat(s,ct)
compare cs to ct strcmp(cs,ct)
only first n chars strncmp(cs,ct,n)
pointer to first c in cs strchr(cs,c)
pointer to last c in cs strrchr(cs,c)
copy n chars from ct to s memcpy(s,ct,n)
copy n chars from ct to s (may overlap) memmove(s,ct,n)
compare n chars of cs with ct memcmp(cs,ct,n)
pointer to first c in first n chars of cs memchr(cs,c,n)
put c into first n chars of s memset(s,c,n)
C Reference Card (ANSI)
Input/Output
Standard I/O
standard input stream stdin
standard output stream stdout
standard error stream stderr
end of file (type is int) EOF
get a character getchar()
print a character putchar(chr)
print formatted data printf("format",arg1,. . . )
print to string s sprintf(s,"format",arg1,. . . )
read formatted data scanf("format",&name1,. . . )
read from string s sscanf(s,"format",&name1,. . . )
print string s puts(s)
File I/O
declare file pointer FILE *fp;
pointer to named file fopen("name","mode")
modes: r (read), w (write), a (append), b (binary)
get a character getc(fp)
write a character putc(chr,fp)
write to file fprintf(fp,"format",arg1,. . . )
read from file fscanf(fp,"format",arg1,. . . )
read and store n elts to *ptr fread(*ptr,eltsize,n,fp)
write n elts from *ptr to file fwrite(*ptr,eltsize,n,fp)
close file fclose(fp)
non-zero if error ferror(fp)
non-zero if already reached EOF feof(fp)
read line to string s (< max chars) fgets(s,max,fp)
write string s fputs(s,fp)
Codes for Formatted I/O: "%-+ 0w.pmc"
- left justify
+ print with sign
space print space if no sign
0 pad with leading zeros
w min field width
p precision
m conversion character:
h short, l long, L long double
c conversion character:
d,i integer u unsigned
c single char s char string
f double (printf) e,E exponential
f float (scanf) lf double (scanf)
o octal x,X hexadecimal
p pointer n number of chars written
g,G same as f or e,E depending on exponent
Variable Argument Lists
declaration of pointer to arguments va_list ap;
initialization of argument pointer va_start(ap,lastarg);
lastarg is last named parameter of the function
access next unnamed arg, update pointer va_arg(ap,type)
call before exiting function va_end(ap);
Standard Utility Functions
absolute value of int n abs(n)
absolute value of long n labs(n)
quotient and remainder of ints n,d div(n,d)
returns structure with div_t.quot and div_t.rem
quotient and remainder of longs n,d ldiv(n,d)
returns structure with ldiv_t.quot and ldiv_t.rem
pseudo-random integer [0,RAND_MAX] rand()
set random seed to n srand(n)
terminate program execution exit(status)
pass string s to system for execution system(s)
Conversions
convert string s to double atof(s)
convert string s to integer atoi(s)
convert string s to long atol(s)
convert prefix of s to double strtod(s,&endp)
convert prefix of s (base b) to long strtol(s,&endp,b)
same, but unsigned long strtoul(s,&endp,b)
Storage Allocation
allocate storage malloc(size), calloc(nobj,size)
change size of storage newptr = realloc(ptr,size);
deallocate storage free(ptr);
Array Functions
search array for key bsearch(key,array,n,size,cmpf)
sort array ascending order qsort(array,n,size,cmpf)
Time and Date Functions
processor time used by program clock()
Example. clock()/CLOCKS_PER_SEC is time in seconds
current calendar time time()
time2-time1 in seconds (double) difftime(time2,time1)
arithmetic types representing times clock_t,time_t
structure type for calendar time comps struct tm
tm_sec seconds after minute
tm_min minutes after hour
tm_hour hours since midnight
tm_mday day of month
tm_mon months since January
tm_year years since 1900
tm_wday days since Sunday
tm_yday days since January 1
tm_isdst Daylight Savings Time flag
convert local time to calendar time mktime(tp)
convert time in tp to string asctime(tp)
convert calendar time in tp to local time ctime(tp)
convert calendar time to GMT gmtime(tp)
convert calendar time to local time localtime(tp)
format date and time info strftime(s,smax,"format",tp)
tp is a pointer to a structure of type tm
Mathematical Functions
Arguments and returned values are double
trig functions sin(x), cos(x), tan(x)
inverse trig functions asin(x), acos(x), atan(x)
arctan(y/x) atan2(y,x)
hyperbolic trig functions sinh(x), cosh(x), tanh(x)
exponentials & logs exp(x), log(x), log10(x)
exponentials & logs (2 power) ldexp(x,n), frexp(x,&e)
division & remainder modf(x,ip), fmod(x,y)
powers pow(x,y), sqrt(x)
rounding ceil(x), floor(x), fabs(x)
Integer Type Limits
The numbers given in parentheses are typical values for the
constants on a 32-bit Unix system, followed by minimum re-
quired values (if significantly different).
CHAR_BIT bits in char (8)
CHAR_MAX max value of char (SCHAR_MAX or UCHAR_MAX)
CHAR_MIN min value of char (SCHAR MIN or 0)
SCHAR_MAX max signed char (+127)
SCHAR_MIN min signed char (−128)
SHRT_MAX max value of short (+32,767)
SHRT_MIN min value of short (−32,768)
INT_MAX max value of int (+2,147,483,647) (+32,767)
INT_MIN min value of int (−2,147,483,648) (−32,767)
LONG_MAX max value of long (+2,147,483,647)
LONG_MIN min value of long (−2,147,483,648)
UCHAR_MAX max unsigned char (255)
USHRT_MAX max unsigned short (65,535)
UINT_MAX max unsigned int (4,294,967,295) (65,535)
ULONG_MAX max unsigned long (4,294,967,295)
Float Type Limits
The numbers given in parentheses are typical values for the
constants on a 32-bit Unix system.
FLT_RADIX radix of exponent rep (2)
FLT_ROUNDS floating point rounding mode
FLT_DIG decimal digits of precision (6)
FLT_EPSILON smallest x so 1.0f + x 6= 1.0f (1.1E− 7)
FLT_MANT_DIG number of digits in mantissa
FLT_MAX maximum float number (3.4E38)
FLT_MAX_EXP maximum exponent
FLT_MIN minimum float number (1.2E− 38)
FLT_MIN_EXP minimum exponent
DBL_DIG decimal digits of precision (15)
DBL_EPSILON smallest x so 1.0 + x 6= 1.0 (2.2E− 16)
DBL_MANT_DIG number of digits in mantissa
DBL_MAX max double number (1.8E308)
DBL_MAX_EXP maximum exponent
DBL_MIN min double number (2.2E− 308)
DBL_MIN_EXP minimum exponent
January 2007 v2.2. Copyright c© 2007 Joseph H. Silverman
Permission is granted to make and distribute copies of this card pro-
vided the copyright notice and this permission notice are preserved on
all copies.
Send comments and corrections to J.H. Silverman, Math. Dept., Brown
Univ., Providence, RI 02912 USA. 〈jhs@math.brown.edu〉
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