了解程序的耗时

测试机器：Intel(R) Core(TM)2 双核， 2.40GHz， memory: 8G

内容：
gettimeofday:    60ns
for(;;):    2.9ns
sprintf():   1.7us [sprintf(buf,"ABCDEF%d",i)]
strcpy():   18ns [size 10]
strcpy():   69120us [size 100,000,000] = 6.9ns [size 10]
memcopy():   43411us [size 100,000,000] = 4.3ns [size 10]
*d=*s:   4.3ns [char *d]

new:   40ns [new(16)]

string +=: 370368us [string +="ABCDEF1234", Total Size=100,000,000]
string.reserve():   220050us [一次分配，测试和上述情况一样]
stringstream <<:   456982us [ <<"ABCDEF1234", Total Size=100,000,000]

string +=: 2664us [string +="ABCDEF1234", Total Size=1,000,000]
string.reserve():   1940us [一次分配，测试和上述情况一样]
stringstream <<:   3595us [ <<"ABCDEF1234", Total Size=1,000,000]

string +=: 77us [string +="ABCDEF1234", Total Size=10,000]
string.reserve():   20us [一次分配，测试和上述情况一样]
stringstream <<:   45us [ <<"ABCDEF1234", Total Size=10,000]

map<string,int>
obj[str]=i:  326407us [1,000,000次]
map<int,int>
obj[i]=i:  109307us [1,000,000次]