ANSI C-文本文件:修改行? [英] ANSI C - Text File: Modify Line?

问题描述

我有这个文本文件:

Line 1. "house"
Line 2. "dog"
Line 3. "mouse"
Line 4. "car"
...

我要更改第2行.在新的第2行中将狗"更改为卡片".

I want to change Line 2. "dog" in new Line 2."cards"

我该怎么办?

谢谢！

(对不起我的英语不好)

(sorry for my bad English)

推荐答案

您的程序可能会这样:

#include <stdio.h>
#include <stdlib.h>

#define MAX_LINE_LENGTH 1000

int main()
{
  FILE * fp_src, *fp_dest;
  char line[MAX_LINE_LENGTH];

  fp_src = fopen("PATH_TO_FILE\\test.txt", "r"); // This is the file to change
  if (fp_src == NULL)
    exit(EXIT_FAILURE);

  fp_dest = fopen("PATH_TO_FILE\\test.txt_temp", "w"); // This file will be created
  if (fp_dest == NULL)
    exit(EXIT_FAILURE);


  while (fgets(line, 1000, fp_src) != NULL) {

    if (strncmp(line, "Line 2.", 7) == 0) {
      fputs("Line 2. \"cards\"\n", fp_dest);
      printf("Applied new content: %s", "Line 2. \"cards\"\n");
    }
    else {
      fputs(line, fp_dest);
      printf("Took original line: %s", line);
    }

  }

  fclose(fp_src);
  fclose(fp_dest);

  unlink("PATH_TO_FILE\\test.txt");
  rename("PATH_TO_FILE\\test.txt_temp", "PATH_TO_FILE\\test.txt");

  exit(EXIT_SUCCESS);
}

在将此解决方案引入某些生产系统时，应注意以下几点:

The following things you should consider when taking this solution into some production system:

• 最大行长是否满足您的需求1000-也许您想提出一种使用 malloc()为一行动态分配内存的解决方案
• 您应该使用一些random-filename-generator来生成临时文件，并确保它不存在，以免覆盖现有文件
• 对于大文件，这种方法可能不是最佳方法，因为您实际上两次将文件内容存储在内存中

• Does the maximum line length of 1000 staisfy your needs - maybe you want to come up with a solution that uses malloc() to dynamically allocate memory for one line
• You should take some random-filename-generator to generate the temporary file and make sure that it doesn't exist yet, so you don't overwrite an existing file
• With large files this approach is maybe not the best because you effectivly have your file-content twice in memory

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