컴파일 환경
x86_64-linux-gnu
gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5)
코드
#include <stdio.h>
#include <string.h>
int main()
{
{
char *str1 = "hello!";
char *str2;
printf("str1(%d): %s\\n", strlen(str1), str1);
str2 = str1;
printf("str2(%d): %s\\n", strlen(str2), str2);
printf("please input a character -> ");
// *str2 = getchar(); // Segmentation fault here
printf("modified str2(%d): %s\\n", strlen(str2), str2);
}printf("\\n");
{
int a = 65;
char *b = &"ABC";
int *c = &"ABC";
printf("a=0x%x, *b=0x%x, *c=0x%x\\n", a, *b, *c);
printf("&a=0x%x, b=0x%x, c=0x%x\\n", &a, b, c);
printf("&\\"ABC\\" is 0x%x\\n", &"ABC");
printf("int value of \\"ABC\\" is 0x%x\\n", *((int *)&"ABC"));
}printf("\\n");
{
typedef struct
{
char a;
char b;
int c;
} user_unpacked_type;
#pragma pack(push, 1);
typedef struct
{
char a;
char b;
int c;
} user_type;
#pragma pop();
printf("size of user_unpacked_type is %d\\n", sizeof(user_unpacked_type));
printf("size of user_type is %d\\n", sizeof(user_type));
{
int i;
user_type ut = {'A', 'B', *((int *)&"CDE")};
for(i=0; i<sizeof(user_type); i++)
printf("ut[%d] is 0x%x\\n", i, ((char *)&ut)[i]);
printf("or otherwise....\n");
for(i=0; i<sizeof(user_type)-sizeof(int); i++)
printf("ut[%d] is 0x%x\\n", i, ((int *)&ut)[i]);
}
}printf("\\n");
{
unsigned int a = 1234567890;
int b = *((int *)&a);
char c = *((char *)&a);
long d = *((long *)&a);
printf("a = 0x%x\\n", a);
printf("b = 0x%x\\n", b);
printf("c = 0x%x\\n", c);
printf("d = 0x%x\\n", d);
}printf("\\n");
return 0;
} |
결과:
// first running str1(6): hello! str2(6): hello! please input a character -> modified str2(6): hello!
a=0x41, *b=0x41, *c=0x434241 &a=0x1ae753b0, b=0x4009c7, c=0x4009c7 &"ABC" is 0x4009c7 int value of "ABC" is 0x434241
size of user_unpacked_type is 8 size of user_type is 6 ut[0] is 0x41 ut[1] is 0x42 ut[2] is 0x43 ut[3] is 0x44 ut[4] is 0x45 ut[5] is 0x0 or otherwise.... ut[0] is 0x44434241 ut[1] is 0x45
a = 0x499602d2 b = 0x499602d2 c = 0xffffffd2 d = 0x499602d2
// second running str1(6): hello! str2(6): hello! please input a character -> modified str2(6): hello!
a=0x41, *b=0x41, *c=0x434241 &a=0xd94056b0, b=0x4009c7, c=0x4009c7 &"ABC" is 0x4009c7 int value of "ABC" is 0x434241
size of user_unpacked_type is 8 size of user_type is 6 ut[0] is 0x41 ut[1] is 0x42 ut[2] is 0x43 ut[3] is 0x44 ut[4] is 0x45 ut[5] is 0x0 or otherwise.... ut[0] is 0x44434241 ut[1] is 0x45
a = 0x499602d2 b = 0x499602d2 c = 0xffffffd2 d = 0x499602d2 |
코드와 실행 결과가 직관적으로 이해가신다면 당신은 C산맥 중 포인터 고개를 반정도 넘으신겁니다...
함수포인터를 다루는 부분이나 구조체간 타입 캐스팅 같은 것들이 아직 남았...ㅠ
근데 그거 끝내면 또 매크로와 레지스터 접근, CPU캐시와 메모리간의 일관성 관리 이슈가 또 있고
하드웨어 깊숙한 곳까지 하드하게 하면 어셈블리 혼성 코딩이 또 있네요(....)
