为什么在mac上itoa()函数不能用呢，引入了stdlib.h

http://www.cplusplus.com/reference/clibrary/cstdlib/itoa/
This function is not defined in ANSI-C and is not part of C++, but is supported by some compilers.
A standard-compliant alternative for some cases may be sprintf:
    * sprintf(str,"%d",value) converts to decimal base.
    * sprintf(str,"%x",value) converts to hexadecimal base.
    * sprintf(str,"%o",value) converts to octal base.
所以说, 这不是支持不支持C++的问题, 而是这个函数本身的问题