sqrt - неудачная функция для примера ловли исключений...
Дело в том, что Борландовская реализация библиотеки math в случае ошибок выплёвывает месажбокс с информацией об ошибке, если не задан обработчик _matherr/_matherrl.
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Prototype

double sqrt(double x);

long double sqrtl(long double x);
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Error handling for these functions can be modified through the functions _matherr and _matherrl.


ну и
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Header File

math.h

Category

Diagnostic Routines, Math Routines

Prototype

int _matherr(struct _exception *e);

int _matherrl(struct _exceptionl *e);

Description

User-modifiable math error handler.

_matherr is called when an error is generated by the math library.

_matherrl is the long double version; it is called when an error is generated by the long double math functions.

_matherr and _matherrl each serve as a user hook (a function that can be customized by the user) that you can replace by writing your own math error-handling routine.

_matherr and _matherrl are useful for information on trapping domain and range errors caused by the math functions. They do not trap floating-point exceptions, such as division by zero. See signal for information on trapping such errors.

You can define your own _matherr or _matherrl routine to be a custom error handler (such as one that catches and resolves certain types of errors); this customized function overrides the default version in the C library. The customized _matherr or _matherrl should return 0 if it fails to resolve the error, or nonzero if the error is resolved. When _matherr or _matherrl return nonzero, no error message is printed and the global variable errno is not changed.
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Ну и поскольку "They do not trap floating-point exceptions, such as division by zero.", пример с делением на 0 работает.