第二部分
第二章
2.55 实现show_bytes
2.56 试着用不同的值运行show_bytes
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| #include <stdio.h>
#include <stdlib.h>
typedef unsigned char *byte_pointer;
void show_bytes(byte_pointer a, int len) {
int i;
for(i=0; i<len; i++) {
printf("%.2x ", a[i]);
}
printf("\\n");
}
int main() {
int a = 123456789;
printf("show int %d\\n", a);
show_bytes((byte_pointer)&a, sizeof(a));
return 0;
}
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2.57 编写show_short, show_long, show_double
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| #include <stdio.h>
#include <stdlib.h>
typedef unsigned char *byte_pointer;
void show_bytes(byte_pointer a, int len) {
int i;
for(i=0; i<len; i++) {
printf("%.2x ", a[i]);
}
printf("\\n");
}
void show_short(short s)
{
printf("the value of short %d is:", s);
show_bytes((char *)&s, sizeof(short));
}
void show_long(long long l)
{
printf("the value of short %lld is:", l);
show_bytes((char *)&l, sizeof(long long));
}
void show_double(double d)
{
printf("the value of short %lf is:", d);
show_bytes((char *)&d, sizeof(double));
}
int main() {
short a = 8;
show_short(a);
long b = 12345678;
show_long(b);
double c = 1234.5678;
show_double(c);
return 0;
}
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2.58 实现is_little_endian
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| #include <stdio.h>
typedef unsigned char *byte_pointer;
int is_little_endian()
{
int val = 0x00000001;
byte_pointer valp = (byte_pointer)&val;
int temp;
temp = valp[0];
if (temp == 1)
return 1;
else
return 0;
}
int main()
{
int result = is_little_endian();
printf("is_little_endian: %d", result);
return 1;
}
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2.59生成一个字，由X的最低有效字节和y剩下的字节组成
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| #include <stdio.h>
typedef unsigned char *byte_pointer;
void show_bytes(byte_pointer a, int len)
{
int i;
for (i = 0; i < len; i++)
{
printf("%.2x ", a[i]);
}
printf("\\n");
}
int main()
{
int x = 0x89ABCDEF;
int y = 0x76543210;
int z = (x & 0xFF) | (y & ~0xFF);
show_bytes((byte_pointer)&z, sizeof(z));
return 1;
}
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2.60
将一个w位的字中的字节从0到w/8-1编号，用C实现返回一个无符号值，其中参数x的字节i位被替换成字节b
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| #include <stdio.h>
#include <inttypes.h>
typedef unsigned char *char_point;
uint32_t replace_byte(uint32_t x, int i, unsigned char b)
{
if (i > 3 || i < 0)
{
return -1;
}
char_point char_date_point = ((char_point)&x) + i;
*char_date_point = b;
printf("result : %X\\r\\n", x);
return x;
}
int main(void)
{
unsigned char replace_data = 0xAB;
uint32_t x = 0x12345678;
uint32_t r_x = 0x12AB5678;
int i_x = 2;
uint32_t y = x;
uint32_t r_y = 0x123456AB;
int i_y = 0;
printf("r_x == result : %d\\r\\n", r_x == replace_byte(x, i_x, replace_data));
printf("r_y == result : %d\\r\\n", r_y == replace_byte(y, i_y, replace_data));
return 1;
}
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