isgreater, isgreaterequal, isless, islessequal, islessgreater, isunordered — floating-point relational tests without exception for NaN


#include <math.h>

int isgreater(x, y);

int isgreaterequal(x, y);

int isless(x, y);

int islessequal(x, y);

int islessgreater(x, y);

int isunordered(x, y);

Link with -lm.

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

All functions described here:



The normal relational operations (like <, "less than") fail if one of the operands is NaN. This will cause an exception. To avoid this, C99 defines the macros listed below.

These macros are guaranteed to evaluate their arguments only once. The arguments must be of real floating-point type (note: do not pass integer values as arguments to these macros, since the arguments will not be promoted to real-floating types).


determines (x) > (y) without an exception if x or y is NaN.


determines (x) >= (y) without an exception if x or y is NaN.


determines (x) < (y) without an exception if x or y is NaN.


determines (x) <= (y) without an exception if x or y is NaN.


determines (x) < (y) || (x) > (y) without an exception if x or y is NaN. This macro is not equivalent to x != y because that expression is true if x or y is NaN.


determines whether its arguments are unordered, that is, whether at least one of the arguments is a NaN.

Return Value

The macros other than isunordered() return the result of the relational comparison; these macros return 0 if either argument is a NaN.

isunordered() returns 1 if x or y is NaN and 0 otherwise.


No errors occur.


For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
isgreater(), isgreaterequal(), isless(), islessequal(), islessgreater(), isunordered() Thread safety MT-Safe

Conforming to

POSIX.1-2001, POSIX.1-2008, C99.


Not all hardware supports these functions, and where hardware support isn't provided, they will be emulated by macros. This will result in a performance penalty. Don't use these functions if NaN is of no concern for you.

See Also

fpclassify(3), isnan(3)


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Referenced By

fpclassify(3), math_error(7).

The man pages isgreaterequal(3), isless(3), islessequal(3), islessgreater(3) and isunordered(3) are aliases of isgreater(3).

2017-09-15 Linux Programmer's Manual