show_bytes:打印任意类型的十六进制表示
代码总览
/* show-bytes - prints byte representation of data */
/* $begin show-bytes */
#include <stdio.h>
/* $end show-bytes */
#include <stdlib.h>
#include <string.h>
/* $begin show-bytes */
typedef unsigned char *byte_pointer;
//typedef char *byte_pointer;
//typedef int *byte_pointer;
void show_bytes(byte_pointer start, size_t len) {
size_t i;
for (i = 0; i < len; i++)
printf("%p\t0x%.2x\n", &start[i], start[i]);
printf("\n");
}
void show_int(int x) {
show_bytes((byte_pointer) &x, sizeof(int));
}
void show_float(float x) {
show_bytes((byte_pointer) &x, sizeof(float));
}
void show_pointer(void *x) {
show_bytes((byte_pointer) &x, sizeof(void *));
}
void test_show_bytes(int val) {
int ival = val;
//float fval = (float) ival;
double fval = (double) ival;
int *pval = &ival;
printf("Stack variable ival = %d\n", ival);
printf("(int)ival:\n");
show_int(ival);
printf("(float)ival:\n");
show_float(fval);
printf("&ival:\n");
show_pointer(pval);
}
void simple_show_a() {
/* $begin simple-show-a */
int val = 0x87654321;
byte_pointer valp = (byte_pointer) &val;
show_bytes(valp, 1); /* A. */
show_bytes(valp, 2); /* B. */
show_bytes(valp, 3); /* C. */
/* $end simple-show-a */
}
void simple_show_b() {
/* $begin simple-show-b */
int val = 0x12345678;
byte_pointer valp = (byte_pointer) &val;
show_bytes(valp, 1); /* A. */
show_bytes(valp, 2); /* B. */
show_bytes(valp, 3); /* C. */
/* $end simple-show-b */
}
void float_eg() {
int x = 3490593;
float f = (float) x;
printf("For x = %d\n", x);
show_int(x);
show_float(f);
x = 3510593;
f = (float) x;
printf("For x = %d\n", x);
show_int(x);
show_float(f);
}
void string_ueg() {
/* $begin show-ustring */
const char *s = "ABCDEF";
show_bytes((byte_pointer) s, strlen(s));
/* $end show-ustring */
}
void string_leg() {
/* $begin show-lstring */
const char *s = "abcdef";
show_bytes((byte_pointer) s, strlen(s));
/* $end show-lstring */
}
void show_twocomp()
{
/* $begin show-twocomp */
short x = 12345;
short mx = -x;
show_bytes((byte_pointer) &x, sizeof(short));
show_bytes((byte_pointer) &mx, sizeof(short));
/* $end show-twocomp */
}
int main(int argc, char *argv[])
{
int val = 12345;
if (argc > 1) {
val = strtol(argv[1], NULL, 0);
printf("calling test_show_bytes\n");
test_show_bytes(val);
} else {
printf("calling show_twocomp\n");
show_twocomp();
printf("Calling simple_show_a\n");
simple_show_a();
printf("Calling simple_show_b\n");
simple_show_b();
printf("Calling float_eg\n");
float_eg();
printf("Calling string_ueg\n");
string_ueg();
printf("Calling string_leg\n");
string_leg();
}
return 0;
}
代码说明
typedef unsigned char *byte_pointer;
将unsigned char命名为byte_pointer
void show_bytes(byte_pointer start, size_t len) {
size_t i;
for (i = 0; i < len; i++)
printf("`%p`\t0x%.2x\n", &start[i], start[i]);
printf("\n");
}
%.2x确保整数都以两位十六进制数输出%p表示指针输出；%d表示输出一个十进制整数；%f表示输出一个浮点数;%c表示输出一个字符\t即Tab键，为制表符，作用是预留八个字节的显示宽度，用于对齐 -start 代表对象的首地址，start[i]表示从start[0]开始的第i个位置处的字节
void show_int(int x) {
show_bytes((byte_pointer) &x, sizeof(int));
}
void show_float(float x) {
show_bytes((byte_pointer) &x, sizeof(float));
}
void show_pointer(void *x) {
show_bytes((byte_pointer) &x, sizeof(void *));
}
这三个函数，将不同类型的指针都强制转化为unsigned char *
void test_show_bytes(int val) {
int ival = val;
//float fval = (float) ival;
double fval = (double) ival;
int *pval = &ival;
printf("Stack variable ival = %d\n", ival);
printf("(int)ival:\n");
show_int(ival);
printf("(float)ival:\n");
show_float(fval);
printf("&ival:\n");
show_pointer(pval);
}
该代码为 测试函数
编译与结果显示
（在Ubuntu 64位的运行结果）
在Linux系统下使用GCC编译该程序
以上为不带参数的运行结果
该图为带参数 3.14的运行结果
解答为何要以unsigned char作为数据类型 当定义为int型时，地址会在正确的地址上加4 当定义为有符号char型时，当最高位为1时，会补符号位
