c++:
using namespace std;
int main(int argc, char*argv[])
{
//此处const 必须有
const char *str = "abcdef";
const char *cmp = "bcdef";
//c++会检测类型，认为这个是常量字符串，如果我们不加const，会报warning
//warning: ISO C++11 does not allow conversion from string literal to 'char *'
//char *str = "abcdef";
//char *cmp = "bcdef";
//下面的方式会引起段错误，因为*ptr不是字符串
// printf("What's *(++str): %c \n ", *(++str));
// printf("What's *cmp: %c \n ", *cmp);
//如下正确，*ptr代表这个指针指向的字符
printf("What's *(++str): %c \n ", *(++str));
printf("What's *cmp: %c \n ", *cmp);
printf("checkout if char equal %d \n", *(str)==*cmp);
//c中，stp和cmp都是指针，我们这样比较，是比较这两个指针值是否相同。
printf("checkout if str equal %d \n", str==cmp);
//这种不经过类型转化的赋值，已经不被允许
//error: cannot initialize a variable of type 'long' with an lvalue of type 'const char *'
//long int t1 = str;
//要想把指针转化成int值，我们要先把它转化成成长整类型
long int t1 = (long int) str;
int t2 =(int)t1;
//在c++中，这种转化方式已经不被允许,因为指针的长度和long int相等。
//int t3 = (int)p_int;
//c++很神奇，如果我们这样写，会报一个warning
printf("what's str int %d \n", str);
//可是，如果我们这样写，会报错
//warning: comparison between pointer and integer ('const char *' and 'int')
// printf("what's str int %d \n", (int)str);
printf("checkout if equal(int to int) %d \n", (long int)str ==t2);
//c++中，str是指针，不能直接和整形数值比较
//printf("checkout if equal(int to str) %d \n", str == t2);
return 0;
}
编译警告：
g++ -std=c++11 c_cpp.cpp -o c_cpp
c_cpp.cpp:37:35: warning: format specifies type 'int' but the argument has type 'const char *' [-Wformat]
printf("what's str int %d \n", str);
~~ ^~~
%s
1 warning generated.
运行结果：
What's *(++str): b What's *cmp: b checkout if char equal 1 checkout if str equal 0 what's str int 118779659 checkout if equal(int to int) 0
c：
#include<stdio.h>
#include<stdlib.h>
int main(int argc, char*argv[])
{
const char *str = "abcdef";
const char *cmp = "bcdef";
//下面的方式会引起段错误，因为*ptr不是字符串
// printf("What's *(++str): %c \n ", *(++str));
// printf("What's *cmp: %c \n ", *cmp);
//如下正确，*ptr代表这个指针指向的字符
printf("What's *(++str): %c \n ", *(++str));
printf("What's *cmp: %c \n ", *cmp);
printf("checkout if char equal %d \n", *(str)==*cmp);
//c中，stp和cmp都是指针，我们这样比较，是比较这两个指针值是否相同。
printf("checkout if str equal %d \n", str==cmp);
int p_int = (int) str ;
printf("what's str int %d \n",(int) str);
printf("what's p_int int %d \n", p_int);
printf("checkout if equal(int to int) %d \n", (int)str == p_int);
//我们用指针和整形值进行比较，会报warning
//warning: comparison between pointer and integer ('const char *' and 'int')
printf("checkout if equal(int to str) %d \n", str == p_int);
return 0;
}
编译警告：
gcc -Wall c_cpp.c -o c_cpp
c_cpp.c:24:55: warning: comparison between pointer and integer ('const char *' and 'int')
printf("checkout if equal(int to str) %d \n", str == p_int);
~~~ ^ ~~~~~
1 warning generate
运行结果：
What's *(++str): b What's *cmp: b checkout if char equal 1 checkout if str equal 0 what's str int 188321487 what's p_int int 188321487 checkout if equal(int to int) 1 checkout if equal(int to str) 0