video cá sấu

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Ngoại lệ (Exception)

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Exception gồm:

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Mơ tả lỗi có thể xảy ra.

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Đoạn mã lệnh trong đó xảy ra exception,

nằm trong khối try{}

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Những thứ gây ra exception nằm trong

lệnh throw

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Ví dụ

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Trong ví dụ về stack, lỗi có thể xảy ra

khi:

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Đẩy nhiều phần tử vào stack

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Lấy phần tử ra khỏi stack rỗng

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Ví dụ …

#include <stdlib.h>

#include <iostream.h>

const int STACK_SIZE = 100;

class stack {

protected:

int count;

private:

int data[STACK_SIZE];

public:

stack(void);

void push(const int item);

int pop(void);

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Ví dụ …

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inline stack::stack(void)

{

count = 0;

}

inline void stack::push(const int item)

{

data[count] = item;

count++;

}

inline int stack::pop(void)

{

count--;

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Ví dụ …

const int WHAT_MAX = 80;

class bound_err {

public:

char what[WHAT_MAX];

bound_err(char *_what) {

if (strlen(_what) < (WHAT_MAX -1))

strcpy(what, _what);

else

strcpy(what, "Internal error: _what is too long");

}

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Ví dụ …

class b_stack: public stack {

public:

void push(const int item) throw(bound_err);

int pop(void) throw(bound_err);

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Ví dụ …

inline void b_stack::push(const int item) throw(bound_err)

{

if (count >= STACK_SIZE)

{

bound_err overflow("Push overflows stack");

throw overflow;

}

stack::push(item);

}

inline int b_stack::pop(void) throw(bound_err)

{

if (count <= 0)

{

throw bound_err("Pop causes stack underflow");

}

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Ví dụ …

b_stack test_stack;
void push_a_lot(void) {

for (int i = 0; i < 5000; i++)
test_stack.push(i);
}
main ()
{
try
{
push_a_lot();
}

catch (bound_err &err)
{

cout << "Error: Bounds exceeded\n";
cout << "Reason: " << err.what << '\n';
exit (8);

}

catch (...)
{

cout << "Error: Unexpected exception occurred\n";
exit (8);

}

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