malloc/free和new/delete的区别
void*；new/delete可自动计算类型的大小，返回对应类型的指针。在C++ Primer书中有提到说： new/delete的表达式与标准库函数同名了，所以系统并没有重载new或delete表达式。new/delete真正的实现其实是依赖下面这几个内存管理接口的。
void *operator new(size_t); //allocate an object void *operator delete(void *); //free an object void *operator new[](size_t); //allocate an array void *operator delete[](void *); //free an array
malloc/free和new/delete的底层实现
new的底层实现
// new.cpp
#include <cstdlib>
#include <new>
_C_LIB_DECL
int __cdecl _callnewh(size_t size) _THROW1(_STD bad_alloc);
_END_C_LIB_DECL
void *__CRTDECL operator new(size_t size) _THROW1(_STD bad_alloc)
{ // try to allocate size bytes
void *p;
while ((p = malloc(size)) == 0)
if (_callnewh(size) == 0)
{ // report no memory
_THROW_NCEE(_XSTD bad_alloc, );
}
return (p);
}
delete的底层实现
#include <cruntime.h>
#include <malloc.h>
#include <new.h>
#include <windows.h>
#include <rtcsup.h>
void operator delete( void * p )
{
RTCCALLBACK(_RTC_Free_hook, (p, 0));
free( p );
}
new[]的底层实现
#include <new>
void *__CRTDECL operator new[](size_t count) _THROW1(std::bad_alloc)
{ // try to allocate count bytes for an array
return (operator new(count));
}
delete[]的底层实现
#ifdef CRTDLL
#undef CRTDLL
#endif
#ifdef MRTDLL
#undef MRTDLL
#endif
#define _USE_ANSI_CPP // suppress defaultlib directive for Std C++ Lib
#include <new>
extern void __CRTDECL operator delete[](void *ptr) _THROW0();
void __CRTDECL operator delete[](void *ptr,
const std::nothrow_t&) _THROW0()
{ // free an allocated object
operator delete[](ptr);
}
malloc/free和new/delete的执行过程
new的执行过程
new(int size) --> operator new() --> malloc() --> constructor function --> return ptr
delete的执行过程
delete ptr --> destructor function --> operator delete() --> free
new[]的执行过程
new[count] --> operator new[]() --> operator new() --> malloc() --> constructor function --> return ptr
delete[]的执行过程
delete[] ptr --> destructor function --> operator delete[]() --> operator delete() --> free
operator delete[]()，operator delete[]()再调用operator deleteoperator delete表达式，依次释放内存operator delete[]()数组的个数存放在指针的前4位参考
