因为平台实时库部分的封装有点小恶心，如果取数据，用户必须传入一个有效的buf的初始地址和长度，接口内部的实现会在长度不够的情况下自动realloc这块buf，所以用户的缓存必须是malloc出来的。部门的个别小伙儿喜欢用了new来分配内存，当然了buf的长度足够大，是不会出问题的，如果一开始分配的比较小，问题就来了。纠结于因为这个问题，老是会被问及C/C++内存管理的差异，特写了个小程序以验证（写的不是很严谨，仅为主题，分别在redhat 5.6 x86_64 + gcc-4.9.2，windows 7 x64 + gcc-4.9.2 编译运行通过）：

代码：

#include <iostream>#include <typeinfo>#include <stdlib.h>#include <stdio.h>void t_cpu(){#define print_type(t) std::cout << "Size of " << #t <<  ": " << sizeof(t) << std::endl    print_type(char);    print_type(unsigned char);    print_type(short);    print_type(unsigned short);    print_type(int);    print_type(unsigned int);    print_type(size_t);    print_type(long);    print_type(unsigned long);    print_type(long long);    print_type(unsigned long long);    print_type(float);    print_type(double);    print_type(long double);    print_type(void*);}void t_new(size_t sl){    class __T {    public:        int _1;        int _2;        __T(){            _1 = 1;            _2 = 2;        }        ~__T(){            printf("~");        }        void test()        {            _1 += _2;        }    };    __T *pchar = new __T[sl];    size_t  *psize  = (size_t*)(((char*)pchar)-sizeof(size_t));    printf("\nTest new and delete \nsize: %ld pchar: %p psize: %p *psize: %ld \n", sl, pchar, psize, *psize);    delete []pchar;    printf("\n");}void t_malloc(size_t sl){    class __T {    public:        int _1;        int _2;        __T(){            _1 = 1;            _2 = 2;        }        ~__T(){            printf("~");        }        void test()        {            _1 += _2;        }    };    printf("\nTest malloc and free \nsize of class __T: %ld  \n", sizeof(class __T));    __T *pchar = (__T *)malloc(sl * sizeof(class __T));    size_t  *psize  = (size_t*)(((char*)pchar)-sizeof(size_t));    printf("size: %ld pchar: %p psize: %p *psize: %ld \n", sl, pchar, psize, *psize);    free(pchar);}void t_new_free(size_t sl){    class __T {    public:        int _1;        int _2;        __T(){            _1 = 1;            _2 = 2;        }        ~__T(){            printf("~");        }        void test()        {            _1 += _2;        }    };    __T *pchar = new __T[sl];    size_t  *psize  = (size_t*)(((char*)pchar)-sizeof(size_t));    printf("\nTest new and free \nsize: %ld pchar: %p psize: %p *psize: %ld \n", sl, pchar, psize, *psize);    //delete []pchar;    for (__T *t = pchar; t < pchar + sl; ++t) {        t->~__T();    }    free(psize);    printf("\n");}void t_malloc_delete(size_t sl){    class __T {    public:        int _1;        int _2;        __T(){            _1 = 1;            _2 = 2;        }        ~__T(){            printf("~");        }        void init()        {            _1 = 7;            _2 = 8;        }        void test()        {            _1 += _2;        }    };    printf("\nTest malloc and delete \nsize of class __T: %ld  \n", sizeof(class __T));    size_t *psize = (size_t *)malloc(sl * sizeof(class __T) + sizeof(size_t));    __T  *pchar  = (__T*)(((char*)psize)+sizeof(size_t));    *psize = sl;    //for (__T *t = pchar; t < pchar + sl; ++t) {    //    t->init();    //}    printf("size: %ld pchar: %p psize: %p *psize: %ld \n", sl, pchar, psize, *psize);    delete [] pchar;    printf("\n");}int main(){    t_cpu();    t_new(48);    t_malloc(32);    t_new_free(16);    t_malloc_delete(8);    return 0;}

输出（redhat）：

Size of char: 1Size of unsigned char: 1Size of short: 2Size of unsigned short: 2Size of int: 4Size of unsigned int: 4Size of size_t: 8Size of long: 8Size of unsigned long: 8Size of long long: 8Size of unsigned long long: 8Size of float: 4Size of double: 8Size of long double: 16Size of void*: 8Test new and delete size: 48 pchar: 0x2442018 psize: 0x2442010 *psize: 48 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Test malloc and free size of class __T: 8  size: 32 pchar: 0x2442010 psize: 0x2442008 *psize: 273 Test new and free size: 16 pchar: 0x2442018 psize: 0x2442010 *psize: 16 ~~~~~~~~~~~~~~~~Test malloc and delete size of class __T: 8  size: 8 pchar: 0x2442018 psize: 0x2442010 *psize: 8 ~~~~~~~~

输出（Windows）：

Size of char: 1Size of unsigned char: 1Size of short: 2Size of unsigned short: 2Size of int: 4Size of unsigned int: 4Size of size_t: 4Size of long: 4Size of unsigned long: 4Size of long long: 8Size of unsigned long long: 8Size of float: 4Size of double: 8Size of long double: 12Size of void*: 4Test new and deletesize: 48 pchar: 00991b54 psize: 00991b50 *psize: 48~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Test malloc and freesize of class __T: 8size: 32 pchar: 00991b50 psize: 00991b4c *psize: 134253675Test new and freesize: 16 pchar: 00991b54 psize: 00991b50 *psize: 16~~~~~~~~~~~~~~~~Test malloc and deletesize of class __T: 8size: 8 pchar: 00991b54 psize: 00991b50 *psize: 8~~~~~~~~

关于 C++ 的 new、delete 与 C 的 malloc、free 的区别