为什么isspace中不能使用参数*it？

Question

vector s = { "asd","sadf","asd"," ","\n" };

for (auto it = s.begin(); it != s.end() && !isspace(*it); ++it)
*it = toupper(*it);

Answer 1

isspace函数的原型是 int isspace(int c); 因为isspace函数是检测一个字符是否是空白符, 上面代码中*it是一个字符串，参数类型不对应所以不可以