替换空格 纯c

class Solution {
public:
    void replaceSpace(char* str, int length)
{
    char* str_new = str;
    int num = 0;
    for (int i = 0; i < length; i++)
    {
        if (str[i] == ' ') {
            num++;
        }
    }
    char* pStr = (char*)malloc(sizeof(char) * length + num*2);
    char* pStr_new = pStr;
    for (int i = 0; i < length; i++)
    {
        if (str[i] == ' ') {
            *(pStr_new++) = '%';
            *(pStr_new++) = '2';
            *(pStr_new++) = '0';
            str_new++;
        }
        else {
            *pStr_new++ = *str_new++;
        }
    }
    strcpy(str, pStr);
}
};