C函数在文件中的特定位置插入文本而不覆盖现有文本 [英] C function to insert text at particular location in file without over-writing the existing text

问题描述

我编写了一个程序，它将一个文件作为输入，每当它找到长度 > 80 的行时，它都会向该文件添加 和 以使其最大宽度为 80 个字符.

I have written a program which takes a file as input and whenever it finds a line with length > 80, it adds and to that file to make it 80 chars in width max.

问题是，每当长度超过 80 时，我都使用 fseek 插入 和 ，因此它会覆盖该行中超过长度 80 的两个字符.有没有一种方法可以插入文本而不覆盖现有的文本?

The problem is that I have used fseek to insert and whenever the length exceeds 80, so it overrides two characters of that line which exceeds length 80. Is there a way using which I can insert text without overriding the existing text?

这是我的代码:-

#include<stdio.h>
#include<string.h>

int main(int argc, char *argv[])
{
  FILE *fp1,*fp2;
  int prev=0,now=0;
  char ch;
  int flag=0;
  long cur;
  fp1=fopen(argv[1],"r+");
  if(fp1==NULL){
    printf("Unable to open the file to read. Program will exit.");
    exit(0);
  }
  else{
    while((ch=fgetc(fp1))!=EOF){
      if(ch!=' ' && ch!='
'){
        now=now+1;
      }
      else{
        if(now>=80){
            fseek(fp1,cur,SEEK_SET);
            fputc('\',fp1);
            fputc('
',fp1);
            now=0;
            continue;
        }
        if(ch=='
'){
          flag=0;
          now=0;
          continue;
          }
        else{
          prev=now;
          cur=ftell(fp1);
        }
        now=now+1;
      }
    }
  }
  fclose(fp1);
  return 0;
}

要运行它，您需要执行以下操作:-

To run it, you need to do following:-

user@ubuntu$ cc xyz.c
user@ubuntu$ ./a.out file_to_check.txt

推荐答案

不，没有办法将字符插入到现有文件中.您将需要使用第二个文件来执行此操作.

No, there's no way to insert characters into an existing file. You will need to use a second file to do that.

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