'rand' 的问题，6.0里面是不是没有这个函数

[angelcm51]

#include <iostream>
#include <cstdlib>
#include <ctime>

using std::cout;
using std::endl;
using std::rand;
using std::srand;
using std::time;

int main() {
const int limit1 = 500; //Upper limit for on set of random values
const int limit2 = 31; //Upper limit for another set of values

cout << "First we will use the default sequence from rand(). \n ";
cout << "Three random integer from 0 to " << RAND_MAX << ": "
<< rand() << " " << rand() << " " <<rand() << endl;
cout << endl << "Now we will use a new seed for rand().\n ";
srand((unsigned int)time(0)); //Set a new seed
cout << "Three random integer from 0 to " << RAND_MAX <<": "
<< rand() << " " <<rand()<<" " << rand()<<endl;

return 0;

}这样子的时候运行不成功，
E:\PROGRAM FILES\LEMOLIANXI\C++入门\Random\random integers.cpp(7) : error C2039: 'rand' : is not a member of 'std'
E:\PROGRAM FILES\LEMOLIANXI\C++入门\Random\random integers.cpp(7) : error C2873: 'rand' : symbol cannot be used in a using-declaration
E:\PROGRAM FILES\LEMOLIANXI\C++入门\Random\random integers.cpp(8) : error C2039: 'srand' : is not a member of 'std'
E:\PROGRAM FILES\LEMOLIANXI\C++入门\Random\random integers.cpp(8) : error C2873: 'srand' : symbol cannot be used in a using-declaration
E:\PROGRAM FILES\LEMOLIANXI\C++入门\Random\random integers.cpp(9) : error C2039: 'time' : is not a member of 'std'
E:\PROGRAM FILES\LEMOLIANXI\C++入门\Random\random integers.cpp(9) : error C2873: 'time' : symbol cannot be used in a using-declaration
执行 cl.exe 时出错.
去掉下面这个就可以了
using std::rand;
using std::srand;
using std::time;
把这个内容去掉就可以运行，而且达到取随机数的效果

为什么用了using后就不可以了呢`？

[cnzdgs]

#include <stdlib.h>

[0黄瓜0]

在VC6中,rand和srand及time没有加入名称空间std中,而是全局的.

#include   <iostream>   
#include   <cstdlib> 
#include   <ctime> 

using   std::cout; 
using   std::endl; 
//using   std::rand; 
//using   std::srand; 
//using   std::time; 

int   main()   { 
    const   int   limit1   =   500;   //Upper   limit   for   on   set   of   random   values 
    const   int   limit2   =   31;   //Upper   limit   for   another   set   of   values 
    
    cout   <<   "First   we   will   use   the   default   sequence   from   rand().   \n   "; 
    cout   <<   "Three   random   integer   from   0   to   "   <<   RAND_MAX   <<   ":   " 
        <<   rand()   <<   "   "   <<   rand()   <<   "   "   <<rand()   <<   endl; 
    cout   <<   endl   <<   "Now   we   will   use   a   new   seed   for   rand().\n   "; 
    srand((unsigned   int)time(0));   //Set   a   new   seed 
    cout   <<   "Three   random   integer   from   0   to   "   <<   RAND_MAX   <<":   " 
        <<   rand()   <<   "   "   <<rand() <<"   "   <<   rand() <<endl; 
    
    return   0; 
    
}

[arong1234]

楼主已经#include <cstdlib>了，因此应该是不行的
而且这种using语法在vc6中是不是也不支持啊？

[ruyunlong2832]

对，应该也可以写#include <cstdlib>的

[angelcm51]

是全局的话,就不需要再用using去声明了吧!

sqrt也是全局的么,最近用的东西怎么都会有这些问题

using反而成了多余的事了

[zhangwanlong]

不用using。。。。

[hu_vane]

4楼正解。
rand、srand、time不属于std的namespace中。
PS：尽量少用using。

[worldli90]

太感谢了，我都忙了半天了

[wangguangjia85]

很是感谢4#及各楼的回答