如何读取和覆盖C文本文件？

Question

我有一个文本文件的text.txt读取（为简单起见）

this is line one 
this is line two 
this is line three 

再次为简单起见，我只是想设置的第一个字符中的每一行以“X”，所以我期望的结果将

xhis is line one 
xhis is line two 
xhis is line three 

所以，我打开text.txt文件，并试图覆盖每行所需的输出到同一文本文件。在while循环中，我将每行中的第一个字符设置为'x'。我还将变量“行”设置为1，因为如果它位于第一行，我想倒回到文件的开头，以便在文件的开头而不是文件末尾进行覆盖。线然后增加，因此它将跳过下一次迭代的倒带，并应继续覆盖第2和第3行。它适用于第一行。

任何人有任何解决方案？顺便说一句，我已经在stackoverflow和其他网站广泛研究了这个，并没有运气。这里是我的代码和我的输出也低于：

#include <stdio.h> 
#include <stdlib.h> 
#define MAX 500 

int main() { 
    char *buffer = malloc(sizeof(char) * MAX); 
    FILE *fp = fopen("text.txt", "r+"); 
    int line = 1; 
    while (fgets(buffer, 500, fp) != NULL) { 
      buffer[0] = 'x'; 
      if (line == 1) { 
        rewind(fp); 
        fprintf(fp, "%s", buffer); 
      } 
      else { 
        fprintf(fp, "%s", buffer); 
      } 
      line++; 
    } 
    free(buffer); 
    fclose(fp); 
} 

输出：

xhis is line one 
this is line two 
xhis is line two 
e 
x 

Answer 1

long pos = ftell(fp);//Save the current position 
while (fgets(buffer, 500, fp) != NULL) { 
    buffer[0] = 'x'; 
    fseek(fp, pos, SEEK_SET);//move to beginning of line 
    fprintf(fp, "%s", buffer); 
    fflush(fp); 
    pos = ftell(fp);//Save the current position 
} 

Answer 2

我总是建议使用其他文件做到这一点kindda解决方案。

1. 阅读线
2. 将X个在生产线中的新文件，并复制该行的其余部分。
3. 做到这一点，直到你得到EOF
4. 删除旧文件
5. 重新命名这个新的文件

Answer 3

尝试了这一点

#include<stdio.h> 
#include<stdio.h> 
#include<string.h> 
int main() 
{ 
    char buffer[500],read[50][50]; 
    FILE *fp=fopen("text.txt","r+"); 
    int line =1; 
    while(fgets(buffer,500,fp)!=NULL){ 
     buffer[0]='x'; 
     printf("\n%d ",line); 
     puts(buffer); 
     strcat(read[line-1],(const char*)buffer); 
     line++; 
    } 
    fclose(fp); 
    FILE *fp1=fopen("text.txt","w"); 
    rewind(fp1); 
    fprintf(fp1,"%s",read); 
    return 0; 
    } 

我工作了这一点，在Windows

Answer 4

// file_overwrite.cpp : main project file. 
// File opens and write y value to a file 
// again reads same file and re-writes y value to a file 

#include "stdafx.h" 

using namespace System; 

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

int main(int argc, char *argv[]) 
{ 
    int x = 19530; 

    FILE *fp1 = fopen("D:\\Data\\BUFF.txt","w+"); 

    if(fp1 == NULL) 
     printf("File not opening \n"); 
     int y=x; 
     fprintf(fp1, "%d \n", y); 
     fclose(fp1); 
     printf("\n file -> open -> write y value and close"); 


     freopen("D:\\Data\\BUFF.txt", "w", fp1); 
     rewind(fp1); 
     y=100; 
     fprintf(fp1, "%d \n", y); 
     printf("\n file -> Reopen -> rewind write y values and close"); 
     fclose(fp1); 

     getch(); 
     return 0; 
} 

Answer 5

// overwrite_file.cpp 
// File opens and write y value to a file 
// again reads same file and re-writes y value to a file 

#include "stdafx.h" 

using namespace System; 

#include<stdio.h> 
#include<stdio.h> 
#include<string.h>    //Include appropriate headers 
#include <conio.h> 
#include<stdlib.h> 

int main(int argc, char *argv[]) 
{ 
    int x = 19530;       // Give any value in the limit 

    FILE *fp1 = fopen("D:\\Data\\BUFF.txt","w+"); // open file to write 

    if(fp1 == NULL)         // if the file pointer encounters a null, it may not open neither overwrite 
     printf("File not opening \n"); 
     int y=x;          
     fprintf(fp1, "%d \n", y);     //print y 
     fclose(fp1); 
     printf("\n file -> open -> write y value and close"); // close the file after writing the value of y 


     freopen("D:\\Data\\BUFF.txt", "w", fp1);   //reopen and rewind file 
     rewind(fp1); 
     y=100;            // this value of y given within the limits gets printed on the .exe console 
     fprintf(fp1, "%d \n", y); 
     printf("\n file -> Reopen -> rewind write y values and close"); // rewind write values and close 
     fclose(fp1); 

     getch(); 
     return 0; 
}