C allows a void* pointer to be assigned to any pointer type without a cast, whereas C++ does not; this idiom appears often in C code using malloc memory allocation. For example, the following is valid in C but not C++:
void* ptr;
int *i = ptr; /* Implicit conversion from void* to int* */
or similarly:
int *j = malloc(sizeof(int) * 5); /* Implicit conversion from void* to int* */
In order to make the code compile in both C and C++, one must use an explicit cast:
void* ptr;
int *i = (int *) ptr;
int *j = (int *) malloc(sizeof(int) * 5);
Source: http://en.wikipedia.org/wiki/Compatibility_of_C_and_C%2B%2B
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2013-11-27 12:30:53