HP OpenVMS SystemsC Programming Language 
Compaq C

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The <errno.h> header file defines several macros used for error reporting.
EDOM
ERANGE
Error codes that can be stored in errno . They expand to integral constant expressions with unique nonzero values.
errno
An external variable or a macro that expands to a modifiable lvalue with type int , depending on the operating system.
The errno variable is used for holding implementationdefined error codes from library routines. All error codes are positive integers. The value of errno is 0 at program startup, but is never set to 0 by any library function. Therefore, errno should be set to 0 before calling a library function and then inspected afterward.
The <limits.h> and <float.h> header files define several macros that expand to various implementationspecific limits and parameters, most of which describe integer and floatingpoint properties of the hardware. See your platformspecific Compaq C documentation for details.
The <locale.h> header file declares two functions and one type and defines several macros.
A structure containing members relating to the formatting of numeric values. The structure contains the following members in any order, with values shown in the comments:
char *decimal_point; /* "." */ char *thousands_sep; /* "" */ char *grouping; /* "" */ char *int_curr_symbol; /* "" */ char *currency_symbol; /* "" */ char *mon_decimal_point; /* "" */ char *mon_thousands_sep; /* "" */ char *mon_grouping; /* "" */ char *positive_sign; /* "" */ char *negative_sign; /* "" */ char int_frac_digits; /* CHAR_MAX */ char frac_digits; /* CHAR_MAX */ char p_cs_precedes; /* CHAR_MAX */ char p_sep_by_space; /* CHAR_MAX */ char n_cs_precedes; /* CHAR_MAX */ char n_sep_by_space; /* CHAR_MAX */ char p_sign_posn; /* CHAR_MAX */ char n_sign_posn; /* CHAR_MAX */
These members are described under the localeconv function in this section.
NULL
LC_ALL
LC_COLLATE
LC_CTYPE
LC_MONETARY
LC_NUMERIC
LC_TIME
Expand to integral constant expressions with distinct values, and can be used as the first argument to the setlocale function.
char *setlocale(int category, const char *locale);
Selects the appropriate portion of the program's locale as specified by the category and locale arguments. This function can be used to change or query the program's entire current locale or portions thereof.
The following values can be specified for the category argument:LC_ALLaffects the program's entire locale.
LC_COLLATEaffects the behavior of the strcoll and strxfrm functions.
LC_CTYPEaffects the behavior of the characterhandling functions and multibyte functions.
LC_MONETARYaffects the monetaryformatting information returned by the localeconv function.
LC_NUMERICaffects the decimalpoint character for the formatted I/O functions and stringconversion functions, as well as the nonmonetary formatting information returned by the localeconv function.
LC_TIMEaffects the behavior of the strftime function.
The following values can be specified for the locale argument:
 "C"specifies the minimal environment for C translation
 ""specifies the use of the environment variable corresponding to category. If this environment variable is not set, the LANG environment variable is used. If LANG is not set, an error is returned.
At program startup, the equivalent of the following is executed:
setlocale(LC_ALL, "C");
The setlocale function returns one of the following:
 If a pointer to a string is specified for locale and the selection can be honored, setlocale returns a pointer to the string associated with the specified category for the new locale. If the selection cannot be honored, setlocale returns a null pointer and the program's locale is not changed.
 If a null pointer is specified for locale, setlocale returns a pointer to the string associated with the category for the program's current locale. The program's locale is not changed.
In either case, the returned pointer to the string is such that a subsequent call with that string value and its associated category will restore that part of the program's locale. This string must not be modified by the program, but it can be overwritten by subsequent calls to setlocale .
struct lconv *localeconv(void);
Sets the components of an object with type struct lconv with values appropriate for formatting numeric quantities according to the rules of the current locale.
The structure members with type char * are pointers to strings, any of which (except decimal_point ) can point to "", which indicates that the value has zero length or is not available in the current locale. Structure members of type char are nonnegative numbers, any of which can be CHAR_MAX to indicate that the value is not available in the current locale. Structure members include the following:char *decimal_pointThe decimalpoint character used to format nonmonetary quantities.
char *thousands_sepThe character used to separate groups of digits before the decimal point in formatted nonmonetary quantities.
char *groupingA string whose elements indicate the size of each group of digits in formatted nonmonetary quantities.
char *int_curr_symbolThe international currency symbol applicable to the current locale. The first three characters contain the alphabetic international currency symbol in accordance with those specified in ISO 4217 Codes for the Representation of Currency and Funds. The fourth character (immediately preceding the null character) is the character used to separate the international currency symbol from the monetary quantity.
char *currency_symbolThe local currency symbol applicable to the current locale.
char *mon_decimal_pointThe decimalpoint character used to format monetary quantities.
char *mon_thousands_sepThe character used to separate groups of digits before the decimal point in formatted monetary quantities.
char *mon_groupingA string whose elements indicate the size of each group of digits in formatted monetary quantities.
char *positive_signThe string used to indicate a nonnegative formatted monetary quantity.
char *negative_signThe string used to indicate a negative formatted monetary quantity.
char int_frac_digitsThe number of fractional digits to be displayed in internationally formatted monetary quantities.
char frac_digitsThe number of fractional digits to be displayed in formatted monetary quantities.
char p_cs_precedesSet to 1 if the currency_symbol precedes the value for a nonnegative formatted monetary quantity; set to 0 if the currency_symbol follows the value.
char p_sep_by_spaceSet to 1 if the currency_symbol is separated by a space from the value for a nonnegative formatted monetary quantity; set to 0 if there is no space.
char n_cs_precedesSet to 1 if the currency_symbol precedes the value for a negative formatted monetary quantity; set to 0 if the currency_symbol follows the value.
char n_sep_by_spaceSet to 1 if the currency_symbol is separated by a space from the value for a negative formatted monetary quantity; set to 0 if there is no space.
char p_sign_posnSet to a value indicating the positioning of the positive_sign for a nonnegative formatted monetary quantity.
char n_sign_posnSet to a value indicating the positioning of the negative_sign for a negative formatted monetary quantity.
The elements of grouping and mon_grouping are interpreted according to the following:
 CHAR_MAX no further grouping is to be performed.
 0the previous element is to be repeatedly used for the remainder of the digits.
 otherthe integer value is the number of digits that comprise the current group. The next element is examined to determine the size of the next group of digits before the current group.
The value of p_sign_posn and n_sign_posn is interpreted as follows:
 0parentheses surround the quantity and currency_symbol
 1the sign string precedes the quantity and currency_symbol
 2the sign string follows the quantity and currency_symbol
 3the sign string immediately precedes the currency_symbol
 4the sign string immediately follows the currency_symbol
The localeconv function returns a pointer to the filled in structure. The structure must not be modified by the program, but might be overwritten by subsequent calls to localeconv or to setlocale with categories LC_ALL , LC_MONETARY , or LC_NUMERIC .
The <math.h> header file defines types, macros, and several mathematical functions. The functions take double arguments and return doubleprecision values.
The behavior of the functions in this header is defined for all representable values of their input arguments. Each function executes as if it were a single operation, without generating any externally visible exceptions.
For all functions, a domain error occurs if an input argument is outside the domain over which the mathematical function is defined. The description of each function lists any domain errors. On a domain error, the function returns an implementationdefined value; the value of the EDOM macro is stored in errno .
For all functions, a range error occurs if the result of the function cannot be represented as a double value. If the result overflows (the magnitude of the result is so large that it cannot be represented in an object of the specified type), the function returns the value of the macro HUGE_VAL , with the same sign (except for the tan function) as the correct value of the function; the value of the ERANGE macro is stored in errno . If the result underflows (the magnitude of the result is so small that it cannot be represented in an object of the specified type), the function returns 0; whether the value of the ERANGE macro is stored in errno is implementationdefined.
Expands to a positive double expression.
Expands to a constant expression of type float representing positive or unsigned infinity, if available; otherwise, expands to a positive constant of type float that overflows at translation time.
Expands to a constant expression of type float representing a quiet NaN.
Returns the value, in radians, of the arc cosine of x in the range [0, pi]. A domain error occurs for arguments not in the interval [  1,+1].
Returns the value, in radians, of the arc sine of x in the range [pi/2,+pi/2]. A domain error occurs for arguments not in the interval [  1,+1].
Returns the value, in radians, of the arc tangent of x in the range [pi/2,+pi/2].
double atan2(double y, double x);
Returns the value, in radians, of the arc tangent of y/x, using the signs of both arguments to determine the quadrant of the return value. The value returned is in the range [pi,+pi]. A domain error may occur if both arguments are 0.
Returns the value, in radians, of the cosine of x.
Returns the value, in radians, of the sine of x.
Returns the value, in radians, of the tangent of x.
Returns the value of the hyperbolic cosine of x. A range error occurs if the magnitude of x is too large.
Returns the value of the hyperbolic sine of x. A range error occurs if the magnitude of x is too large.
Returns the value of the hyperbolic tangent of x.
Exponential and Logarithmic Functions
Returns the value of the exponential function of x. A range error occurs if the magnitude of x is too large.
double frexp(double value, int *eptr);
Breaks the floatingpoint number value into a normalized fraction in the interval [1/2, 1) or 0, which it returns, and an integral power of 2, which it stores in the int object pointed to by eptr. If value is 0, both parts of the result are 0.
double ldexp(double x, int exp);
Multiplies a floatingpoint number by an integral power of 2, and returns the value x x 2^{exp}. A range error may occur.
Returns the natural logarithm of x. A domain error occurs if the argument is negative. A range error may occur if the argument is 0.
Returns the baseten logarithm of x. A domain error occurs if x is negative. A range error may occur if x is 0.
double modf(double value, double *iptr);
Breaks the argument value into integral and fractional parts, each of which has the same sign as the argument. The modf function returns the signed fractional part and stores the integral part as a double in the object pointed to by iptr.
double pow(double x, double y);
Returns the value x^{y}. A domain error occurs if x is negative and y is not an integral value. A domain error occurs if the result cannot be represented when x is 0 and y is less than or equal to 0. A range error may occur.
Returns the nonnegative square root of x. A domain error occurs if x is negative.
Nearest Integer, Absolute Value, and Remainder Functions
Returns the smallest integral value not less than x.
Returns the absolute value of a floatingpoint number x.
Returns the largest integral value not greater than x.
double fmod(double x, double y);
Computes the floatingpoint remainder of x/y. The fmod function returns the value x  i * y, for some integer i such that if y is nonzero, the result has the same sign as x and magnitude less than the magnitude of y. The function returns 0 if y is 0.
The <setjmp.h> header file contains declarations that provide a way to avoid the normal function call and return sequence, typically to permit an intermediate return from a nested function call.
Sets up the local jmp_buf buffer and initializes it for the jump (the jump itself is performed with longjmp .) This macro saves the program's calling environment in the environment buffer specified by the env argument for later use by the longjmp function. If the return is from a direct invocation, setjmp returns 0. If the return is from a call to longjmp , setjmp returns a nonzero value.
jmp_buf
An array type suitable for holding the information needed to restore a calling environment.
Restores the context of the environment buffer env that was saved by invocation of the setjmp function in the same invocation of the program. The longjmp function does not work if called from a nested signal handler; the result is undefined.
The value specified by value is passed from longjmp to setjmp . After longjmp is completed, program execution continues as if the corresponding invocation of setjmp had just returned value. If value is passed to setjmp as 0, it is converted to 1.
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