从文件中读取一个字符串，直到我们在 c/c++ 中得到 '\n' 字符或 EOF

Question

我想打开两个文件并将这些字符串保存到第三个文件中，这些字符串存在于第一个文件中但不存在于第二个文件中。为此，我必须逐行读取字符串（即直到我到达下一行字符）。但是对于文件的最后一行我最后没有 '\n' 因为有 EOF 。所以，请帮助我读取文件的所有字符串然后存储在字符数组中..

代码：-

#include<stdio.h>
#include<string.h>
int main()
{
FILE *f1ptr,*f2ptr,*f3ptr;
f1ptr=fopen("1stfile.txt","r");
f3ptr=fopen("3rdfile.txt","w");
char arr1[100],arr2[100];
while(fscanf(f1ptr," %[^\n]",arr1)!=EOF)    
    {
    f2ptr=fopen("2ndfile.txt","r");
    int flag=1;
    while(fscanf(f2ptr," %[^\n]",arr2)!=EOF)
        {
        if(strcmp(arr1,arr2) ==0)
            {
            flag=0;//flag=0 means i will not store this string into file
            }
        }
    fclose(f2ptr);
    if(flag)
        fprintf(f3ptr,"%s\n",arr1);
    }
return 0;
}

我的文件如下 第一个文件

 Minimum Points To Reach Destination
 Maximum Index
 Maximum of minimum for every window size
 Find Prime numbers in a range
 Largest Number formed from an Array
 Find sum of different corresponding bits for all pairs
 Rearrange an array with O(1) extra space
 Return two prime numbers
 Sorting Elements of an Array by Frequency 
 A Simple Fraction 
 QuickSort on Doubly Linked List
 Reorder List
 Binary Tree to DLL
 Tree from Postorder and Inorder

第二个文件

 Maximum Index
 Find Prime numbers in a range
 Rearrange an array with O(1) extra space
 Return two prime numbers
 Sorting Elements of an Array by Frequency

Answer 1

以下可能有效。如果使用 fgets，最后一行将添加 '\n'。

#include<stdio.h>
#include<string.h>
//using namespace std;
int main()
{
    FILE *f1ptr,*f2ptr,*f3ptr;
    f1ptr=fopen("1stfile.txt","r");
    f3ptr=fopen("3rdfile.txt","w");
    char arr1[100],arr2[100];

    while (fgets(arr1, 100, f1ptr) != NULL) {
        f2ptr=fopen("2ndfile.txt","r");
        int flag=1;
        while (fgets(arr2, 100, f2ptr)!=NULL) {
            if (strcmp(arr1,arr2) ==0) {
                flag=0;  //flag=0 means i will not store this string into file   
            }
        }
        fclose(f2ptr);
        if (flag)
            fprintf(f3ptr,"%s",arr1);
    }

    return 0;
}

Answer 2

这是使用 rewind() 的解决方案。

f1ptr=fopen("1stfile.txt","r");
//Check f1ptr is not NULL.
f2ptr=fopen("2ndfile.txt","r");
//Check f2ptr is not NULL.
f3ptr=fopen("3rdfile.txt","w");
//Check f3ptr is not NULL.
char arr1[100],arr2[100];

while(fgets(arr1, sizeof arr1, f1ptr) )   
{
    int flag=1;
    rewind(f2ptr);  //Moves file pointer to the top.
    while(fgets(arr2,sizeof arr2, f2ptr))
    {
        if(strcmp(arr1,arr2) ==0)
        {
           flag=0;//flag=0 means i will not store this string into file
           break;  //Break out of the loop if 2 files have the same line.
        }
    }
    if(flag)
       fprintf(f3ptr,"%s",arr1);  //No need to print newline. Its already there.
  }
  fclose(f1ptr);
  fclose(f2ptr);
  fclose(f3ptr);

如果man fgets，这里有一部分描述：fgets()从stream中读入最多一个小于size的字符，存入s指向的buffer中。在 EOF 或换行符后停止阅读。如果读取到换行符，则将其存储到缓冲区中。终止空字节 ('[=14=]') 存储在缓冲区中的最后一个字符之后。

所以换行符被添加到字符串而不是 EOF。

从文件中读取一个字符串，直到我们在 c/c++ 中得到 '\n' 字符或 EOF

read a string from the file till we get '\n' character or EOF in c/c++

c

file-handling