V7/usr/man/man3/assert.3x

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.TH ASSERT 3X
.SH NAME
assert \-
program verification
.SH SYNOPSIS
.B #include <assert.h>
.PP
.B assert (expression)
.SH DESCRIPTION
.PP
.I Assert
is a macro that indicates
.I expression
is expected to be true at this point in the program.
It causes an
.IR exit (2)
with a diagnostic comment on the standard output
when
.I expression
is false (0).
Compiling with the 
.IR cc (1)
option
.SM
.B \-DNDEBUG
effectively deletes
.I assert
from the program.
.SH DIAGNOSTICS
`Assertion failed: file
.I f
line
.I n.'
.I F
is the source file and
.I n
the source line number
of the
.I assert
statement.