C# string.Format 与+性能比较

string date = DateTime.Now.ToString("yyyy-MM-dd hh:mm:ss fff ");

string DATETIME_FORMAT = string.Empty;

for (int i = 0; i < 500; i++)
{
　　string DATE_FORMAT = "yyyy-MM-dd";
　　DATETIME_FORMAT = DATETIME_FORMAT+string.Format("{0} {1} {2} {3} HH:mm:ss", DATE_FORMAT, " HH:mm:ss", " HH:mm:ss", "HH:mm:ss");
}
date = date + DateTime.Now.ToString("yyyy-MM-dd hh:mm:ss fff ");
string DATETIME_FORMAT2 = string.Empty;
for (int i = 0; i < 500; i++)
{
　　string DATE_FORMAT = "yyyy-MM-dd";
　　DATETIME_FORMAT2 = DATETIME_FORMAT2 + DATE_FORMAT + " HH:mm:ss" + " HH:mm:ss" + " HH:mm:ss" + " HH:mm:ss";
}
date = date + DateTime.Now.ToString("yyyy-MM-dd hh:mm:ss fff ");

date运行结果2012-09-11 05:39:16 964  2012-09-11 05:39:16 980   2012-09-11 05:39:16 985

string date = DateTime.Now.ToString("yyyy-MM-dd hh:mm:ss fff ");
for (int i = 0; i < 500000; i++)
{
　　string DATE_FORMAT = "yyyy-MM-dd";
　　string DATETIME_FORMAT = string.Format("{0} {1} {2} {3} HH:mm:ss", DATE_FORMAT, " HH:mm:ss", " HH:mm:ss", " HH:mm:ss");
}
date = date + DateTime.Now.ToString("yyyy-MM-dd hh:mm:ss fff ");

for (int i = 0; i < 500000; i++)
{
　　string DATE_FORMAT = "yyyy-MM-dd";
　　string DATETIME_FORMAT2 = DATE_FORMAT + " HH:mm:ss" + " HH:mm:ss" + " HH:mm:ss" + " HH:mm:ss";
}
date = date + DateTime.Now.ToString("yyyy-MM-dd hh:mm:ss fff ");

date运行结果2012-09-11 05:42:52 563 2012-09-11 05:42:52 837 2012-09-11 05:42:52 873

从以上两段代码可以看出 +的性能要比string.Format 高很多