# 添字演算子Subscripting

## 例Example

``````// subscripting.cpp
// compile with: /EHsc
#include <iostream>

using namespace std;
class IntVector {
public:
IntVector( int cElements );
~IntVector() { delete [] _iElements; }
int& operator[](int nSubscript);
private:
int *_iElements;
int _iUpperBound;
};

// Construct an IntVector.
IntVector::IntVector( int cElements ) {
_iElements = new int[cElements];
_iUpperBound = cElements;
}

// Subscript operator for IntVector.
int& IntVector::operator[](int nSubscript) {
static int iErr = -1;

if( nSubscript >= 0 && nSubscript < _iUpperBound )
return _iElements[nSubscript];
else {
clog << "Array bounds violation." << endl;
return iErr;
}
}

// Test the IntVector class.
int main() {
IntVector v( 10 );
int i;

for( i = 0; i <= 10; ++i )
v[i] = i;

v[3] = v[9];

for ( i = 0; i <= 10; ++i )
cout << "Element: [" << i << "] = " << v[i] << endl;
}
``````
``````Array bounds violation.
Element: [0] = 0
Element: [1] = 1
Element: [2] = 2
Element: [3] = 9
Element: [4] = 4
Element: [5] = 5
Element: [6] = 6
Element: [7] = 7
Element: [8] = 8
Element: [9] = 9
Array bounds violation.
Element: [10] = 10
``````

`i`前のプログラムでが10に達すると、 operator [] は、範囲外の添字が使用されていることを検出し、エラーメッセージを発行します。When `i` reaches 10 in the preceding program, operator[] detects that an out-of-bounds subscript is being used and issues an error message.