运行时报错：
terminate called after throwing an instance of 'std::out_of_range'
what(): basic_string::substr：__pos
Aborted (core dumped)
内存读取越界。
解释1：for example:
const std::string sTest( "test" );
sTest.substr( 0, 10 );
will raise the same exception, since you ask 10 characters, but only 5 ( sTest.length()) ) are available.
调试过，正常运行，无报错。
解释2：
Chances are you did something like:
std::string s("foo");
s.substr(5,1); //the length of the string is 3, 5 is out of bounds
调试过，确实会报错，out_of_range
解决方案：查找substr方法前后代码，排除可能的越界条件。
