Question

我目前有一个文件将新条目附加到当前文件。我想获取最近的5个条目。如何在C中首先读取最后一行？如果可能的话，我想使用fgets命令逐行读取。

感谢您的帮助！

编辑：例如：

原始档案：

The cat is fast.
Dogs are cool.
I like pie.

期望的输出：

I like pie.
Dogs are cool.
The cat is fast.

Answer 1

while(fgets(buffer,sizeof(buffer),fp); //go on scanning lines

//Now `buffer` holds the last line of `fp`

Answer 2

#include <stdio.h>

#define N 5 //number of recent entry

int main(void){
    long entry[N+1];//+1 for end of file
    int i, index = 0;
    FILE *fp = fopen("entry.txt", "r");
    char line[128];

    for(i=0;i<N+1;++i)
        entry[i] = -1L;//initialize to invalid value

    do{ //path I : store file position
        entry[index++] = ftell(fp);
        if(index == N+1)
            index = 0;
    }while(EOF!=fscanf(fp, "%*[^\n]%*c"));

    if(--index < 0)//one back index
        index += N+1;
    entry[index] = -1L;//for end of file

    for(i = 0; i < N; ++i){//get N entry
        if(--index < 0)
            index += N+1;
        if(entry[index] < 0L)
            break;//when number of entry < N
        fseek(fp, entry[index], SEEK_SET);
        fgets(line, sizeof line, fp);
        fputs(line, stdout);
    }
    fclose(fp);
    return 0;
}

首先在C中读取文件的最后一行

2 个答案: