C ++无法将解引用的char指针与char比较

Question

I have an input string, and I want to find how many spaces are there in the string.

Here's my code

// input string
std::string str = "abc d e f";

// convert string to cstring
char* cstr = new char[str.length()+1];
std::strcpy(cstr, str.c_str());

// iterate through the cstring and count how many spaces are there
int num_of_spaces = 0;
char* ptr = cstr;

while (ptr) {
    if (*ptr == ' ') {
        ++num_of_spaces;
    }
    ++ptr;
}

However, I got an error message on the if (*ptr == ' ') line that says: Thread 1: EXC_BAD_ACCESS (code = 1, address=0x100200000)

Isn't *ptr a char type value because ptr is a char* pointer and I dereferenced it to *ptr . If so, why the comparison is not valid?

Answer 1

您不希望while (ptr) ， while (*ptr)想要while (*ptr) ，也就是说，虽然ptr指向的不是一个零字符，它标志着C样式字符串的结尾。