如何在处理输入文件时向前看(处理2行) [英] How to peek ahead when processing an input file (processing 2 lines)

问题描述

在逐行浏览文本文件时，我希望能够向前看下一行，并在处理当前行的同时检查它。我正在用C语言工作。我相信fseek()或其他类似的功能会对我有帮助，但我不确定，也不知道如何使用它们。我想取得的成就是：

    fp = fopen("test-seeking.txt", "r");

    while((fgets(line, BUFMAX, fp))) {
        // Peek over to next line
        nextline = ...;
        printf("Current line starts with: %-3.3s / Next line starts with %-3.3s
",
               line, nextline);
    }

感谢您的帮助。

推荐答案

确实可以使用fseek并尝试这样的操作：

fp = fopen("test-seeking.txt", "r");

while ((fgets(line, BUFMAX, fp))) {
    // Get the next line
    fgets(nextline, BUFMAX, fp);

    // Get the length of nextline
    int nextline_len = strlen(nextline);

    // Move the file index back to the previous line
    fseek(fp, -nextline_len, SEEK_CUR); // Notice the - before nextline_len!

    printf("Current line starts with: %-3.3s / Next line starts with %-3.3s
", line, nextline);
}

---

另一种方法是使用fgetpos和fsetpos，如下所示：

fp = fopen("test-seeking.txt", "r");

while ((fgets(line, BUFMAX, fp))) {
    // pos contains the information needed from
    //   the stream's position indicator to restore
    //   the stream to its current position. 
    fpos_t pos;

    // Get the current position
    fgetpos(fp, &pos);

    // Get the next line
    fgets(nextline, BUFMAX, fp);

    // Restore the position
    fsetpos(fp, &pos);

    printf("Current line starts with: %-3.3s / Next line starts with %-3.3s
", line, nextline);
}

这篇关于如何在处理输入文件时向前看(处理2行)的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！