C语言实现的程序，读取并打印文件最后N行

tail.c

#include <stdio.h>

/*
 * Author: Leslie Zhu
 * Email: [email protected]
 */

/*
 * @num  : the last num line of file to display
 * @files: a file list
 * @len  : the length of @files list
 *
 * @return: void
 *
 *
 * sum of the '\n' to get the position of last @num line,
 * thus display the last @num line one by one
 */
void tail(int num, char *files[],int len){
    FILE *fp;

    char buf[1024];
    char ch;

    int i = 0;
    int pos = 0;
    int count = 0;
    int length = 0;


    for (i=0; i < len; i++){
        fp = fopen(files[i],"r");

        if (NULL == fp){
            printf("Can not open file %s\n",files[i]);
        }    

        if(1 < len){
            printf("==> %s <==\n",files[i]);
        }

        pos = -1;
        count = 0;
        length = 0;

        while(count <= num){
            if(ftell(fp) == (SEEK_SET+1)){
                fseek(fp,0,SEEK_SET);
                break;
            }

            fseek(fp,pos,SEEK_END);
            pos -= 1;
            ch = fgetc(fp);
            
            if(ch == '\n'){
                count += 1;
            }
            
            if(length == 0){
                length = ftell(fp);
            }

        }

        while(feof(fp) != 1){
            if (ftell(fp) == length){
                break;
            }

            fgets(buf,1024,fp);
            printf("%s",buf);
            fflush(fp);
        }

        fclose(fp);
    }
        
}

int main(int argc, char **argv){
    
    char *files[argc];
    int i = 1;
    
    if (3 > argc){
        printf("Usage: %s num FILE1 [FILE2..]\n", argv[0]);
        return -1;
    }
    
    for (i = 2; i < argc; i++){
        files[i-2] = argv[i];
    }
    
    tail(atoi(argv[1]),files,argc-2);
    
    return 0;
}