assert

assert

Put Diagnostics into Programs

Portability: ISO/ANSI C conforming, UNIX compatible

SYNOPSIS
DESCRIPTION
RETURN VALUE
CAUTION
USAGE NOTES
EXAMPLE
RELATED FUNCTIONS
SEE ALSO

SYNOPSIS

#include <assert.h>

void assert(int expr);

DESCRIPTION

assert puts diagnostics into programs. expr is an expression. If the macro name NDEBUG is undefined at the point in the source file where <assert.h> is included, then assert expands to a statement that tests the expression. If the expression is false (that is, compares equal to 0), assert writes the text of the argument, the source filename as defined by __FILE__ , and the source line number as defined by __LINE__ to stderr (the standard error file). It then calls abort .

If NDEBUG is defined at the point in the program where <assert.h> is included, then assert expands to (void *)0 .

The diagnostic is in the format of a normal library diagnostic, with the following text:

Assertion failed: expr
Interrupted while: Executing line number of source-file

expr is the expression, number is the current value of __LINE__ , and source-file is the current value of __FILE__ .

RETURN VALUE

assert has no return value.

CAUTION

assert generates a library diagnostic. Because the quiet function suppresses library diagnostics, it also suppresses assert diagnostics.

You should suppress assertions by defining NDEBUG , not by calling quiet ; quiet will have no effect on the run-time overhead of verifying the assertions.

USAGE NOTES

The macro NDEBUG is automatically defined by the compiler, unless you use the DEBug option. Suppress this automatic definition by using the UNdef option or by using NDEBUG in a #undef preprocessor directive. If you use the DEBug option, then NDEBUG is not automatically defined.

EXAMPLE

#include <math.h>
#include <assert.h>
#include <stdio.h>

double arcsin(double x)  {
   assert(x <= 1.0 && x >= -1.0);
   return asin(x);
}

main()
{
   double num, svalue;

   puts("Enter a number.");
   scanf("%f",#);
   svalue = arcsin(num);
   printf("The arcsin of the number is %f \n", svalue);
}

RELATED FUNCTIONS

quiet

SEE ALSO

Diagnostic Control Functions

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