Retrieve the legitimate string in a bunch of data, first read a data read into the cache of the buffsize and then retrieve in the cache.
When testing such a program, when the amount of data used is insufficient, the program output is correct, but in fact defects. Because of the reason for the programming, some places such as heads, tails, or other special places may not be retrieved in certain places, such as heads, tails, or other special places. A good test should use a sufficient amount of data to ensure that the legal string appears once in each location of the cache.
