C++ fill 和memset

以下内容来自www.cplusplus.com---------------------------------------------------

FILL:

template <class ForwardIterator, class T>
  void fill (ForwardIterator first, ForwardIterator last, const T& val);

Fill range with value

Assigns val to all the elements in the range [first,last).

The behavior of this function template is equivalent to:

template <class ForwardIterator, class T>
  void fill (ForwardIterator first, ForwardIterator last, const T& val)
{
  while (first != last) {
    *first = val;
    ++first;
  }
}

MEMSET:

void * memset ( void * ptr, int value, size_t num );

Fill block of memorySets the first num bytes of the block of memory pointed by ptr to the specified value (interpreted as an unsigned char).------------------------------------------------------------------------------------------------------

可以看出：fill是按元素填充而memset是按字节填充.

代码如下：

#include<iostream>
#include<cstring>
using namespace std;
int main(void)
{
        int  test[100];
        fill(test,test+100,1);
        cout<<"case 1:"<<endl;
        for(int i=0;i<100;i++)
           cout<<test[i]<<" ";
        cout<<endl;
        memset(test,1,sizeof(test));
        cout<<"case 2:"<<endl;
        for(int i=0;i<100;i++)
            cout<<test[i]<<" ";
        cout<<endl;
        memset(test,1,100*sizeof(int));
        cout<<"case 3:"<<endl;
        for(int i=0;i<100;i++)
            cout<<test[i]<<" ";
        cout<<endl;
}

运行结果如下：

fill按元素填充，所以数组里有100个1；

memset按字节填充，int有四个字节，1*2^24+1*2^16+1*2^8+1*2^0=16843009,数组里有100个16843009

哦？所以说清零的话fill和memset一样了？