课堂练习2

一、xxd的使用

二、

xxd的主要功能是将文件转化为十六进制显示，通过man xxd可以得到，需要使用unistd.h实现

三、伪代码

openfile
readbyte
0x
new text
print 0x

四、

include <stdio.h>

include <stdlib.h>

include <string.h>

void print_hex_dump(FILE *file, long offset, int length) {
fseek(file, offset, SEEK_SET);

unsigned char buffer[length];
size_t bytesRead = fread(buffer, 1, length, file);

if (bytesRead == 0) {
printf("Error reading file.\n");
return;
}

printf("File Length: %ld bytes\n", bytesRead);

for (size_t i = 0; i < bytesRead; i++) {
printf("%02X ", buffer[i]);
}
printf("\n");
}

int main(int argc, char *argv[]) {
if (argc != 4) {
printf("Usage: %s \n", argv[0]);
printf("Options:\n");
printf(" -h n Display the first n bytes of the file.\n");
printf(" -t n Display the last n bytes of the file.\n");
return 1;
}

int n = atoi(argv[2]);
if (n <= 0) {
printf("Invalid value for n. Please provide a positive integer.\n");
return 1;
}

char *filename = argv[3];
FILE *file = fopen(filename, "rb");

if (!file) {
printf("Error opening file: %s\n", filename);
return 1;
}

if (strcmp(argv[1], "-h") == 0) {
print_hex_dump(file, 0, n);
} else if (strcmp(argv[1], "-t") == 0) {
fseek(file, 0, SEEK_END);
long fileLength = ftell(file);
long offset = (fileLength - n) >= 0 ? (fileLength - n) : 0;
print_hex_dump(file, offset, n);
} else {
printf("Invalid option: %s\n", argv[1]);
fclose(file);
return 1;
}

fclose(file);
return 0;
}