如何在c中寫入文件的特定行？

Question

因此，我有一個正在執行的項目，並且創建了一個程序，該程序允許用戶寫入文件，如下所示：

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

 FILE *fd;
 FILE *fw;

     struct store
     {
          char Word[512];
          char NWord[512];
     }
     stock;

     struct store2
     {
          char Definition[512];
     }
     stock2;

char done='y';
int count=1;
int c=0;
int d=0;

int main(void)
{
    fw=fopen("Test Z W.txt","w");
    fd=fopen("Test Z D.txt","w");

    do
    {    
         printf("Word %d: ",count);
         gets(stock.Word);
         while((c= getchar()) != '\n' && c != EOF);

         printf("Definition %d: ",count);
         gets(stock2.Definition);
         while((c= getchar()) != '\n' && c != EOF);  

         fprintf(fw,"%s\n", stock.Word);         
         fprintf(fd,"%s\n", stock2.Definition);        
         count=count+1;  
         system("cls");                
    }
    while (count<11);

fclose(fd);
fclose(fw);

return 0;

}

這段代碼很好，但是，我想對其進行擴展，以便可以僅編輯一個選定的行，而不是擦除整個文件並再次寫入所有內容。

我要做的就是使用如何在C語言中寫入txt文件的特定行？

這不是很有幫助，因為我無法回答問題並將其導入到我的代碼中，無論哪種方式，我所需要的都是可以輕松修復以下錯誤的東西。

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系統將自動詢問用戶要編輯的行。

Answer 1

#include <stdio.h>
int main()
{
    FILE *fp,*fc;
    int lineNum;  //stores line number which should be edited.
    int count=0;  //count number lines in source file.
    int ch;   //temporary place to store character of source file(one at a time).
    int edited=0;  //0=false and 1=true
    int t;   //temporary place to store input which you want to be replaced with error in text file.


    fp=fopen("source.txt","r");
    fc=fopen("target.txt","w");

    if(fp==NULL||fc==NULL)
    {
        printf("\nError...cannot open/create files");
        return 1;
    }

    printf("\nEnter Line Number Which You Want 2 edit: ");
    scanf("%d",&lineNum);

    while((ch=fgetc(fp))!=EOF)
    {
        if(ch=='\n')  //counts number of lines
            count++;
        if(count==lineNum-1 && edited==0)  //if specific line(error line) is found and that line is still not edited. More Explanation:- If we want to edit 3rd line than we should start writing at the end of 2nd line(hence count==lineNum-1) and edited==0 means that error line is still not edited. 
        {
            printf("\nEnter input to store at line %d:",lineNum);

            scanf(" %c",&t);  //You can replace this statement with any input operation which you want to replace it with the error line.

            if(count==0)  //if its the first line to edit..
                fprintf(fc,"%s\n",t)   //watch closely,no '\n' before %s,This will copy without creating a extra newline in beginning of new file.
            else 
                fprintf(fc,"\n%s\n",t);  //stores input at error line in file fc(target.txt) from variable t.

            edited=1;  //this prevents loop to execute more than once(as error is already edited),so there will be no need to execute this loop till the end of program

            while( (ch=fgetc(fp))!=EOF )  //Actually this loop will skips the existing line in source.txt(see below)
            {                           //we want to skip this line because this is error line.
                if(ch=='\n')//this will break when next new line(after error line is skipped) is found.
                    break;
            }
       }
       else
          fprintf(fc,"%c",ch);
    }
    fclose(fp);
    fclose(fc);

    if(edited==1)
        printf("\nCongrates...Error Edited Successfully.");
    else
        printf("\nLine Not Found");

return 0;
}

該程序將打開一個源文件（ 可能有錯誤 ，我將其稱為source.txt *），並不斷逐字符讀取並寫入新文件（target.txt），直到找到（EOF）。但是它將停止在特定行，並要求用戶輸入一些數據，這些數據將代替錯誤（源文件中的錯誤行）寫入新文本文件（target.txt）中。

因此，最后您將獲得沒有錯誤的target.txt文件。 打開並檢查它。

在這個程序中，我假設我們只想替換第3行的單個字符，但是您可以更改此操作以將其替換為字符串，浮點數或整數等。

這是輸出：-

輸入您想要的行號2編輯：3

輸入輸入以存儲在第3行：3

聚合...錯誤已成功編輯。

target.txt的內容：-

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