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By default operator new will throw a std::bad_alloc exception if the allocation fails. Therefore you need not check that the result of operator new is NULL. However, to ease conversion of code to C++, the C++ Standard ISO/IEC 14882-2003 provides a variant of operator new that behaves like malloc():

charint* s = new charint[-1]; // throws a std::bad_alloc exception
charint* s = new (std::nothrow) charint[-1]; // returns NULL

When using std::nothrow, it is imperative to check that the return value is not NULL before using it.

Noncompliant Code Example (malloc())

In this example, input_string array is copied into dynamically allocated memory referenced by str copy. However, the result of malloc() is not checked before str copy is referenced. Consequently, if malloc() fails, the program abnormally terminates.

charint *input_stringarray;
size_t size;

/* initialize input_string array and size */

size_t size = strlen(input_string) + 1;
charint *strcopy = (char *)malloc(size * sizeof(int));
strcpy(str, input_stringmemcpy( copy, array, size * sizeof(int));
/* ... */
free(strcopy);
strcopy = NULL;

Noncompliant Code Example (std::nothrow)

This example remains noncompliant if we replace malloc() with new(std::nothrow).

charint *input_stringarray;
size_t size;

/* initialize input_string array and size */

size_t size = strlen(input_string) + 1;
char *strint *copy = new(std::nothrow) charint[size];
strcpy(str, input_stringmemcpy( copy, array, size * sizeof(int));
/* ... */
delete[] strfree(copy);
strcopy = NULL;

Compliant Solution (std::nothrow)

With std::nothrow, the new operator returns either a null pointer or a pointer to the allocated space. Always test the returned pointer to ensure it is not NULL before referencing the pointer. Handle the error condition appropriately when the returned pointer is NULL.

charint *input_stringarray;
size_t size;

/* initialize input_string array and size */

size_t size = strlen(input_string) + 1;
charint *strcopy = new(std::nothrow) charint[size];
if (strcopy == NULL) {
  /* Handle allocation error */
}
 else {
  strcpy(str, input_stringmemcpy( copy, array, size * sizeof(int));
  /* ... */
  delete[] strfree(copy);
  strcopy = NULL;
}

Compliant Solution (bad_alloc)

Alternatively, one can use operator new without std::nothrow. Unless std::nothrow is provided, operator new never returns NULL; it will instead throw a std::bad_alloc exception if it cannot allocate memory.

charint *input_stringarray;
size_t size;

/* initialize input_string array and size */

size_t size = strlen(input_string) + 1;
char *strint *copy = new charint[size];
strcpy(str, input_stringmemcpy( copy, array, size * sizeof(int));
/* ... */
delete[] strfree(copy);
strcopy = NULL;

Risk Assessment

Failing to detect allocation failures can lead to abnormal program termination and denial-of-service attacks.

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