C:带有const修饰的指针解读
通过实例来看看const所修饰的指针使用方法：
1、
先看一个普通的指针使用。
形式：int *pTmp
含义：一个普通的指向int类型的指针
[cpp]
int main(int argc, char *argv[])
{
int i = 1;
int *pTmp = &i;
printf("pTmp = %d/n", *pTmp);
i = 2;
printf("pTmp = %d/n", *pTmp);
(*pTmp)++;
printf("pTmp = %d/n", *pTmp);
system("PAUSE");
return 0;
}
int main(int argc, char *argv[])
{
int i = 1;
int *pTmp = &i;
printf("pTmp = %d/n", *pTmp);
i = 2;
printf("pTmp = %d/n", *pTmp);
(*pTmp)++;
printf("pTmp = %d/n", *pTmp);
system("PAUSE");
return 0;
}
输出：
[plain]
pTmp = 1
pTmp = 2
pTmp = 3
请按任意键继续. . .
pTmp = 1
pTmp = 2
pTmp = 3
请按任意键继续. . .
没有任何问题，pTmp指针你可以任意操作。
2、
形式：const int *pTmp
含义：表示pTmp所指向的对象是只读的，但pTmp可指向其他地址，即pTmp可变。
[cpp]
int main(int argc, char *argv[])
{
int i = 1;
int j = 100;
const int *pTmp = &i; /*正确：表示pTmp所指向的对象是只读的，但pTmp可指向其他地址，即pTmp可变*/
printf("pTmp = %d/n", *pTmp);
i = 2;
printf("pTmp = %d/n", *pTmp);
pTmp = &j; /*正确：将pTmp指向变量j的地址*/
printf("pTmp = %d/n", *pTmp);
(*pTmp)++; /*错误,pTmp指向的对象是只读的，编译出错提示：assignment of read-only location */
printf("pTmp = %d/n", *pTmp);
system("PAUSE");
return 0;
}
int main(int argc, char *argv[])
{
int i = 1;
int j = 100;
const int *pTmp = &i; /*正确：表示pTmp所指向的对象是只读的，但pTmp可指向其他地址，即pTmp可变*/
printf("pTmp = %d/n", *pTmp);
i = 2;
printf("pTmp = %d/n", *pTmp);
pTmp = &j; /*正确：将pTmp指向变量j的地址*/
printf("pTmp = %d/n", *pTmp);
(*pTmp)++; /*错误,pTmp指向的对象是只读的，编译出错提示：assignment of read-only location */
printf("pTmp = %d/n", *pTmp);
system("PAUSE");
return 0;
}
3、
形式：int const *pTmp
含义：与2相同， 表示pTmp所指向的对象是只读的，但pTmp可指向其他地址，即pTmp可变。
[cpp]
int main(int argc, char *argv[])
{
int i = 1;
int j = 100;
const int *pTmp = &i; /*正确：表示pTmp所指向的对象是只读的，但pTmp可指向其他地址，即pTmp可变*/
printf("pTmp = %d/n", *pTmp);
i = 2;
printf("pTmp = %d/n", *pTmp);
pTmp = &j; /*正确：将pTmp指向变量j的地址*/
printf("pTmp = %d/n", *pTmp);
(*pTmp)++; /*错误,pTmp指向的对象是只读的，编译出错提示：assignment of read-only location */
printf("pTmp = %d/n", *pTmp);
system("PAUSE");
return 0;
}
int main(int argc, char *argv[])
{
int i = 1;
int j = 100;
const int *pTmp = &i; /*正确：表示pTmp所指向的对象是只读的，但pTmp可指向其他地址，即pTmp可变*/
printf("pTmp = %d/n", *pTmp);
i = 2;
printf("pTmp = %d/n", *pTmp);
pTmp = &j; /*正确：将pTmp指向变量j的地址*/
printf("pTmp = %d/n", *pTmp);
(*pTmp)++; /*错误,pTmp指向的对象是只读的，编译出错提示：assignment of read-only location */
printf("pTmp = %d/n", *pTmp);
system("PAUSE");
return 0;
}
4、
形式：int * const pTmp
含义：pTmp不可修改，但pTmp所指向的对象可以修改。
[cpp]
int main(int argc, char *argv[])
{
int i = 1;
int j = 100;
int * const pTmp = &i;
printf("pTmp = %d/n", *pTmp);
i = 2;
printf("pTmp = %d/n", *pTmp);
pTmp = &j; /*错误，pTmp不可修改，编译提示：error:assignment of read-only variable `pTmp'*/
printf("pTmp = %d/n", *pTmp);
(*pTmp)++; /*正确，pTmp所指向的对象可以修改 */
printf("pTmp = %d/n", *pTmp);
system("PAUSE");
return 0;
}
int main(int argc, char *argv[])
{
int i = 1;
int j = 100;
int * const pTmp = &i;
printf("pTmp = %d/n", *pTmp);
i = 2;
printf("pTmp = %d/n", *pTmp);
pTmp = &j; /*错误，pTmp不可修改，编译提示：error:assignment of read-only variable `pTmp'*/
printf("pTmp = %d/n", *pTmp);
(*pTmp)++; /*正确，pTmp所指向的对象可以修改 */
printf("pTmp = %d/n", *pTmp);
system("PAUSE");
return 0;
}
5、
形式：const int * const pTmp
含义：pTmp不可修改，pTmp所指对象也不能修改。
[cpp]
int main(int argc, char *argv[])
{
int i = 1;
int j = 100;
const int * const pTmp = &i;
printf("pTmp = %d/n", *pTmp);
i = 2; /*正确*/
printf("pTmp = %d/n", *pTmp);
pTmp = &j; /*错误：error: assignment of read-only variable `pTmp'*/
printf("pTmp = %d/n", *pTmp);
(*pTmp)++; /*错误：error: increment of read-only location*/
printf("pTmp = %d/n", *pTmp);
system("PAUSE");
return 0;
}
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