sizeof

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本文详细解析了C++中sizeof运算符的使用方法及其特点。通过多个示例代码展示了如何获取不同数据类型、数组、指针及引用的大小，并解释了在32位操作系统下基本数据类型的字节长度。

// 扩展了 c++ primer中的代码,加了一些自己的注释
#include <iostream>
using namespace std;
int main() {
size_t ia;
    ia = sizeof( ia );     // ok
    ia = sizeof ia;        // ok
    // ia = sizeof int;    // error
    ia = sizeof( int );    // ok

    int *pi = new int[ 12 ]; // pi是指针变量,而不是数组名
    cout << "pi: " << sizeof( pi )
         << " *pi: " << sizeof( *pi )
         << endl;

    // a string's size is independent of
    // of the length of the string it addresses

    string st1( "foobar" );
    string st2( "a might oak" );
    string *ps = &st1;

    cout << "st1: " << sizeof( st1 )
         << " st2: " << sizeof( st2 )
         << " ps: " << sizeof( ps )
         << " *ps: " << sizeof( *ps )
         << endl;
   char *d_str = new char[3];
   d_str[0] = 'A';d_str[1] = 'b';d_str[2] = '/0';
   cout << "d_str:/t"<< sizeof(d_str) << endl; //4
   cout << "*d_str:/t"<< sizeof(*d_str) << endl;//1

    cout << "short :/t"    << sizeof(short)    << endl; //2
    cout << "short* :/t"   << sizeof(short*)   << endl; //4
    cout << "short& :/t"   << sizeof(short&)   << endl; //2
    cout << "short[3] :/t" << sizeof(short[3]) << endl; //6

   int arr[] ={4,8,9,5,6}; // ia不可改变,可用数组名求其数组大小
   int *parr = arr;
   cout << "arr :/t" << sizeof(arr) << endl; // 20，是数组名,而不是指针
   cout << "parr :/t"<< sizeof(parr) << endl; // 变量,只能求其指针大小//4
   cout << "*parr :/t"<<sizeof(*parr) << endl; // 4

   char str_c[] ={"china"};
   char *p_str = str_c;
   cout << "str_c" << sizeof(str_c) << endl; //6 字符串也按数组计算大小
   cout << "p_str" << sizeof(p_str) << endl; //4
   cout << "*p_str"<< sizeof(*p_str) << endl; // 1

}

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在32位操作系统中,基本数据类型

类型字节长度

char 1

short 2

short int 2

signed short 2

unsigned short 2

int 4

long int 4

signed int 4

unsigned int(unsigned) 4

long 4