constant
std::nothrow
<new>
extern const nothrow_t nothrow;
Nothrow constant
This constant value is used as an argument for
operator new and
operator new[] to indicate that these functions shall not throw an exception on failure, but return a null pointer instead.
By default, when the
new operator is used to allocate memory and the handling function is unable to do so, a
bad_alloc exception is thrown. But when
nothrow is used as argument for
new, it returns a null pointer instead.
This constant (
nothrow) is just a value of type
nothrow_t, which only purpose is to trigger an overloaded version of function
operator new or
operator new[] that takes an argument of this type.
In C++, the
new operator can be overloaded to take more than one parameter: The first parameter passed to the
operator new function is always the size of the element type to be allocated, but more arguments can be passed to this function by enclosing them in parentheses. For example:
is a valid expression that, at some point, calls:
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operator new (sizeof(int),x);
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By default, one of the versions of
operator new is overloaded to accept a parameter of type
nothrow_t (like
nothrow). The value itself is not used, but that version of
operator new shall return zero in case of failure instead of throwing an exception.
The same applies for operator
new[] and function
operator new[] .
Example
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
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// nothrow example
#include <iostream>
#include <new>
using namespace std;
int main () {
cout << "Attempting to allocate 1 MiB...";
char* p = new (nothrow) char [1048576];
if (p==0) cout << "Failed!\n";
else {
cout << "Success!\n";
delete[] p;
}
return 0;
}
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See also
- operator new
- Allocate storage space (function
)