1-1-file-reverse.c

#include<stdio.h>
#include<stdlib.h>
#include<sys/stat.h>
#include<sys/types.h>
#include<fcntl.h>
#include<unistd.h>
#define SIZE_4K 1024*4

int getFileSize(char * strFileName)
{
	int size;
	FILE *fp = fopen(strFileName, "r");
	fseek(fp, 0L, SEEK_END);
	size = ftell(fp);
	fclose(fp);

	return size;
}

void revere_string(char*str, int len)
{
	int i;
	char temp_char;
	for (i = 0; i < len / 2; i++)
	{
		temp_char = str[i];
		str[i] = str[len - i - 1];
		str[len - i - 1] = temp_char;
	}
}

int main()
{
	int len = getFileSize("4kb.txt");
	char buf[len];
	int fd;
	fd = open("4kb.txt", O_RDWR);

	if (fd == -1)
	{
		return -1;
	}
	else
	{
		read(fd, buf, 1);
	}
	close(fd);

	if ((fd = open("4kb.txt", O_RDWR)) == -1)
	{
		return -1;
	}
	else
	{
		revere_string(buf, len);
		write(fd, buf, 1);
	}
	close(fd);
	return 0;
}