字符常量包含多个字符的一点思考--有疑问
一。先写段程序来看下机器的大端小端
1 #include<stdio.h>
2 /*函数checkCPU判断计算机是使用大端存储还是小端*/
3 int checkCPU()
4 {
5 union w{
6 int a;
7 char b;
8 }c;
9 c.a = 1;
10
11 return(c.b == 1); //如果是小端的话，则程序返回1
12 }
13
14 int main()
15 {
16 int b = checkCPU();
17 if(1 == b)
18 {
19 printf("Little Endian!/n"); //小端
20 }
21 else
22 {
23 printf("Big Endian! /n");
24 }
25 return 0;
26 }
编译：gcc testEndian.c -o testEndian
执行结果：
Little Endian!
二。当一个字符常量包含多个字符赋值给一个char类型变量
说明：在第一部分已经测试了机器是使用小端存储，就是高位存储在高地址，地位存储在低地址
1 #include<stdio.h>
2
3 int main()
4 {
5 char ch;
6
7 ch = '123'; //编译时候有警告warning: multi-character character constant ;warning: overflow in implicit constant conversion
8 printf("the char ch is %c /n" ,ch); //输出是3，因为是小端字节序;
9
10 ch = 'abc'; //编译时候有警告
11 printf("the char ch is %c /n" ,ch);
12
13 return 0;
14 }
编译：gcc testChar1.c -o testChar1
执行结果：
the char ch is 3
the char ch is c
三。一个字符常量包含多个字符，直接打印输出 --不明白？
1 #include<stdio.h>
2
3 int main()
4 {
5 char *pt = '12'; //编译有警告：initialization makes pointer from integer without a cast
//注意：这里不是char *pt = "12";
6 printf("the bits of the CPU is %d bits/n/n" ,sizeof(pt) * 8);
7 printf("the adress of pt is %p /n" ,pt);
8 printf("the content of 'printf(" " ,'12');'is 0x %x:/n/n" ,'12'); //
warning: multi-character character constant
9 // printf("%d" ,*pt); // 为什么会有段错误呢？？
10
11 char *ps = '56'; //可以理解成把'56'对应的ASCII码对应的十六进制当成地址赋值给指针变量ps??
12 printf("the adress of ps is %p /n" ,ps);
13 printf("the content of 'printf(" " ,'56');'is 0x%x :/n/n" ,'56');
14
15 char *pp = '98765'; //warning:
character constant too long for its type ,
16 printf("the address of ps is %p /n" ,pp);
17 printf("the content of 'printf(" " ,'98765');'is 0x%x :/n" ,'98765');//
warning: character constant too long for its type
18
19 return 0;
20 }
编译：
beanu@beanu-laptop:~/work/day10.22$ gcc testChar.c
testChar.c:5:13: warning: multi-character character constant
testChar.c: In function ‘main’:
testChar.c:5: warning: initialization makes pointer from integer without a cast
testChar.c:8:61: warning: multi-character character constant
testChar.c:11:13: warning: multi-character character constant
testChar.c:11: warning: initialization makes pointer from integer without a cast
testChar.c:13:61: warning: multi-character character constant
testChar.c:15:13: warning: character constant too long for its type
testChar.c:15: warning: initialization makes pointer from integer without a cast
testChar.c:17:62: warning: character constant too long for its type
执行结果：
the bits of the CPU is 32 bits
the adress of pt is 0x3132
the content of 'printf( ,'12');'is 0x 3132 :
the adress of ps is 0x3536
the content of 'printf( ,'56');'is 0x3536 :
the address of ps is 0x38373635
the content of 'printf( ,'98765');'is 0x38373635 :
----
个人拙见：printf("%x" , '12'); 是打印出来这个地址对应的十六进制数