- 4.67.2.5. -
Table of Contents
4. Standard Units
4.67. System - Built-in routines
4.67.2. System Unit Procedures and Functions
4.67.2.5. Assert procedure
4.67.2.5. Assert procedure
Targets: MS-DOS, OS/2, Win32
System Unit
Procedure Assert tests whether a Boolean expression is true.
Declaration:
procedure Assert(expr: Boolean);
Remarks:
Assert takes a Boolean expression (expr) as parameter.
If the Boolean test fails, Assert raises an Assertion Failed run-time error.
The Assert procedure is typically used to identify logic errors during
program development, by implementing the expr argument to evaluate to
FALSE only when the program is operating incorrectly. After debugging is
complete, assertion checking can be turned off without modifying the source
file by defining the $C
compiler directive.
Assert prints a diagnostic message when expr evaluates to FALSE
and terminates program execution. No action is taken if expr is TRUE.
The diagnostic message includes the name of the source file and line number
where the assertion failed.
Example:
uses Strings; (* Tests a string to see if it is nil, *)
(* empty, or longer than 2 characters *)
procedure AnalyzeString (s: PChar);
begin
Assert(s <> nil); // Cannot be nil
Assert(s[0] <> #0); // Cannot be empty
Assert(StrLen(s) > 2); // Length must exceed 2
end;
var
test1: PChar := 'abc';
test2: PChar := nil;
test3: PChar := '';
begin
Writeln('Analyzing string ', test1);
AnalyzeString(test1);
Writeln('Analyzing string ', test2);
AnalyzeString(test2);
Writeln('Analyzing string ', test3);
AnalyzeString(test3);
end.
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