memset效率问题

char buff[10]

初始化一个字符数组，只需要buff[0] = '\0'即可，没有必要用memset，在使用该buff时，需要注意末尾加'\0'，这样性能比较好。

 #include <iostream>
 #include "sys/time.h"

 void use_memset()
 {
     timeval timestart,timeend;
     gettimeofday(×tart, NULL);

     for( int i = 0; i < 512; i ++)
     {
         char* buff = new char[1024*1024];
         memset(buff,0,1024*1024);
         delete[] buff;
     }

     gettimeofday(&timeend, NULL);
     double linStart = 0,linEnd = 0;
     linStart = ((double)timestart.tv_sec * 1000000 + (double)timestart.tv_usec);    //unit S
     linEnd = ((double)timeend.tv_sec * 1000000 + (double)timeend.tv_usec);       //unit S
     double time = linEnd-linStart;
     printf("%f/n",time);
 }

 void use_setlast()
 {
     timeval timestart,timeend;
     gettimeofday(×tart, NULL);

     for( int i = 0; i < 512; i ++)
     {
         char* buff = new char[1024*1024];
         buff[1024*1024-1] = '/0';
         delete[] buff;
     }

     gettimeofday(&timeend, NULL);
     double linStart = 0,linEnd = 0;
     linStart = ((double)timestart.tv_sec * 1000000 + (double)timestart.tv_usec);    //unit S
     linEnd = ((double)timeend.tv_sec * 1000000 + (double)timeend.tv_usec);       //unit S
     double time = linEnd-linStart;
     printf("%f/n",time);
 }

 int main(int argc, char** argv)
 {
     use_memset();
     use_setlast();
 }

运行结果：
502575.000000
5342.000000
相差100倍。因此，能确定长度或者大概长度的情况下，请不要memset所有字符。