150. Evaluation of inverse Polish expression

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Reverse Polish notation
Q：atoi（） Functions and .c_str() What is the role ？ Why write like this ？
A:
Source code ：stk.push(atoi(token.c_str()));
atoi() Express ascii to integer) Is a function that converts a string to an integer
Function is int atoi(const char * nptr)
It can be seen that , Biography is char type , So be right token Use .c_str(),C++ Use in string Class represents a string ,string Class c_str Method can be returned with C Linguistic char * String in the form of .