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C does not provide direct support to exception handling: it is the programmer's responsibility to prevent errors in the first place and test return values from the functions.
In computer programming, several language mechanisms exist for exception handling. The term exception is typically used to denote a data structure storing information about an exceptional condition. One mechanism to transfer control, or raise an exception, is known as a throw; the exception is said to be thrown. Execution is transferred to a catch.
An exception handling mechanism allows the procedure to raise an exception [2] if this precondition is violated, [1] for example if the procedure has been called on an abnormal set of arguments. The exception handling mechanism then handles the exception. [3] The precondition, and the definition of exception, is subjective.
The raise statement, used to raise a specified exception or re-raise a caught exception; The class statement, which executes a block of code and attaches its local namespace to a class, for use in object-oriented programming; The def statement, which defines a function or method
For example, y == 0 or x/y > 100 will never raise a divide-by-zero exception. These operators return the value of the last operand evaluated, rather than True or False. Thus the expression (4 and 5) evaluates to 5, and (4 or 5) evaluates to 4.
In this C# example, all exceptions are caught regardless of type, and a new generic exception is thrown, keeping only the message of the original exception. The original stacktrace is lost, along with the type of the original exception, any exception for which the original exception was a wrapper, and any other information captured in the ...
In a language with exceptions, a natural type for the raise construct is raise ∈ exception -> Bot, and similarly for other control structures. Intuitively, Bot here is the type of computations that do not return an answer. Bot is useful in typing the "leaf nodes" of polymorphic data structures.
In Python, some built-in types (numbers, Booleans, strings, tuples, frozensets) are immutable, but custom classes are generally mutable. To simulate immutability in a class, one could override attribute setting and deletion to raise exceptions: