将文本插入特定行

Question

我正在尝试创建一个根据用户输入在行与行之间插入文本的函数。用户必须指定行号和索引才能插入他的行。

目前，我已经设法在行前插入文本，但无法将其插入行"index"。有谁知道如何根据索引号插入？ PS。我仍然是 C 编程的初学者。我知道打开和关闭文件的次数太多了！

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

void inserttext(void);

main ()
{
    inserttext();
}    

void inserttext(void)
{
    FILE *file1,*file2;
    char *f = malloc(sizeof(char)), *t = malloc(sizeof(char));
    int l,i,r,y,n,index,nl=0;

    printf("Enter a text file name: ");
    scanf("%s",f);

    if (access(f,F_OK)!=-1)//if the text file exists
    {
        file1=fopen(f, "r+");
        file2=fopen("f2.txt", "w+");
        printf("\nThe file before editing:\n\n");
        while((n=fgetc(file1))!=EOF)// to show the contents of the file before the edit
        {
            putchar(n);
        }
        fclose(file1);
        fclose(file2);

        if(access(f,W_OK)!=-1)//if the file has the write permission
        {
            file1=fopen(f, "r+");
            file2=fopen("f2.txt", "w+");

            printf("\n\nPlease enter your text: \n");
            scanf(" %[^\n]s ",t);

            printf("Specify the line number where you want to insert: ");
            scanf("%d", &l);

            printf("\nindex:\n");
            scanf("%d", &index);

            while((r=fgetc(file1))!=EOF)//copying file1 contents into file2 contents
            {
                fputc(r,file2);
                if(r == '\n' && ++nl == l){
                    fprintf(file2, "%s ", t);//adding the inserted text
                }
            }
            fclose(file1);
            fclose(file2);

            file1=fopen(f, "w+");
            file2=fopen("f2.txt", "r");
            while((y=fgetc(file2))!=EOF){
                    fputc(y,file1);
            }
            fclose(file2);
            fclose(file1);
            remove("f2.txt");

            file1=fopen(f, "r");
            printf("\n");
            while((i=fgetc(file1))!=EOF)//showing the result after inserting
            {
                putchar(i);
            }
            fclose(file1);
            free(f);
            free(t);
            }
            else{
            printf("\n%s text file does not have the Write Permission!", f);
            free(f);
            free(t);
            return;
                }
            }else{
                printf("file doesn't exits!\n");
            }
}

Answer 1

这里使用ftell()和fseek()保存所选行开始的文件位置，读取行的长度和return到行的开始。
提示用户在小于行长度的行中输入索引。我确实遇到了 *t 和 *f 的原始 malloc 的分段错误。我尝试了一些更长的输入，所以这为每个指针分配了 100 个字符。

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

void inserttext(void);

int main ()
{
    inserttext();
    return 0;
}

void inserttext(void)
{
    FILE *file1,*file2;
    char *f = malloc(100), *t = malloc(100);
    int l,i,r,y,n,index,nl=0;
    int linelength = 0;;
    long offset = 0;

    printf("Enter a text file name: ");
    scanf("%99s",f);

    if (access(f,F_OK)!=-1)//if the text file exists
    {
        file1=fopen(f, "r+");
        file2=fopen("f2.txt", "w+");
        printf("\nThe file before editing:\n\n");
        while((n=fgetc(file1))!=EOF)// to show the contents of the file before the edit
        {
            putchar(n);
        }
        fclose(file1);
        fclose(file2);

        if(access(f,W_OK)!=-1)//if the file has the write permission
        {
            file1=fopen(f, "r+");
            file2=fopen("f2.txt", "w+");

            printf("\n\nPlease enter your text: \n");
            scanf(" %99[^\n]",t);

            printf("Specify the line number where you want to insert: ");
            scanf("%d", &l);

            while((r=fgetc(file1))!=EOF)//copying file1 contents into file2 contents
            {
                fputc(r,file2);
                if(r == '\n' && ++nl == l){
                    offset = ftell ( file1);//save location in file
                    while ( ( r = fgetc ( file1)) != '\n' && r != EOF) {
                        linelength++;//count characters in line
                    }
                    fseek ( file1, offset, SEEK_SET);//seek  back to start of line
                    //get index where to insert text
                    do {
                        printf("\nindex(less than %d):\n", linelength);
                        if ( ( scanf("%d", &index)) != 1) {
                            scanf ( "%*[^\n]");//input not an integer. clear buffer
                            index = linelength;
                        }
                    } while ( index >= linelength || index < 0);

                    while ( index) {
                        r = fgetc ( file1);
                        fputc(r,file2);
                        index--;
                    }
                    fprintf(file2, "%s ", t);//adding the inserted text
                }
            }
            printf("\nDONE:\n");
            fclose(file1);
            fclose(file2);

            file1=fopen(f, "w+");
            file2=fopen("f2.txt", "r");
            while((y=fgetc(file2))!=EOF){
                    fputc(y,file1);
            }
            fclose(file2);
            fclose(file1);
            remove("f2.txt");

            file1=fopen(f, "r");
            printf("\n");
            while((i=fgetc(file1))!=EOF)//showing the result after inserting
            {
                putchar(i);
            }
            fclose(file1);
            free(f);
            free(t);
        }
        else{
            printf("\n%s text file does not have the Write Permission!", f);
            free(f);
            free(t);
            return;
        }
    }else{
        printf("file doesn't exits!\n");
    }
}

将文本插入特定行

Inserting a text into a specific line

c

codeblocks