c - 如何将o/p存储到缓冲区中，然后从缓冲区存储到文件

Question

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

int compare (const void *a, const void * b){  
  return ( *(char *)a - *(char *)b ); }

// A utility function two swap two characters a and b
  void swap (char* a, char* b)
{
char t = *a;
*a = *b;
*b = t;  }

int findCeil (char str[], char first, int l, int h)
{
   // initialize index of ceiling element
    int ceilIndex = l;
    int i;
// Now iterate through rest of the elements and find
// the smallest character greater than 'first'
for (i = l+1; i <= h; i++)
  if (str[i] > first && str[i] < str[ceilIndex])
        ceilIndex = i;

return ceilIndex;   
 }


// Print all permutations of str in sorted order
void sortedPermutations ( char str[] )
 {
   FILE *fp;
   fp = fopen("out.txt","w+"); 
   char buffer[100];
   memset(buffer,'\0',100);
   // Get size of string
      int size = strlen(str);
  // Sort the string in increasing order
      qsort( str, size, sizeof( str[0] ), compare );

   // Print permutations one by one
   bool isFinished = false;
   while ( ! isFinished )
    {
    // print this permutation
    setvbuf(str, buffer, _IONBF, 1024);
    printf ("%s \n", str);
    fprintf(fp,"%s\n",buffer);
    // Find the rightmost character which is smaller than its next
    // character. Let us call it 'first char'
    int i;
    for ( i = size - 2; i >= 0; --i )
       if (str[i] < str[i+1])
          break;

    // If there is no such chracter, all are sorted in decreasing order,
    // means we just printed the last permutation and we are done.
    if ( i == -1 )
        isFinished = true;
    else
    {
        // Find the ceil of 'first char' in right of first character.
        // Ceil of a character is the smallest character greater than it
        int ceilIndex = findCeil( str, str[i], i + 1, size - 1 );

        // Swap first and second characters
        swap( &str[i], &str[ceilIndex] );

        // Sort the string on right of 'first char'
        qsort( str + i + 1, size - i - 1, sizeof(str[0]), compare );
    }
 fclose(fp);
  }
 }

int main()
 {



char str[] = "ABCD";
sortedPermutations( str );

return 0;
 }

嗨，我正在尝试困惑求解器。我想将排列结果存储到缓冲区，然后从缓冲区存储到某个文件，以便我可以将其与字典进行比较。 setvbuf 出现错误。我的C很生疏，达不到想要的结果。

Answer 1

有很多错误。首先，您使用带有错误参数的 setvbuf 并循环执行此操作。然后你 fprintf 缓冲区值而不是 str。并且循环关闭文件。

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

int compare (const void *a, const void * b) {  
    return ( *(char *)a - *(char *)b ); 
}

void swap (char* a, char* b) {
    char t = *a;
    *a = *b;
    *b = t;  
}

int findCeil (const char str[], char first, int l, int h) {
    int ceilIndex = l;
    int i;
    for (i = l+1; i <= h; i++) {
        if (str[i] > first && str[i] < str[ceilIndex]) {
            ceilIndex = i;
        }
    }
    return ceilIndex;   
}

void sortedPermutations ( char str[] ) {
    FILE *fp;
    char buffer[1024];
    int size = strlen(str);
    int isFinished = 0;

    fp = fopen("out.txt","w+"); 
    memset(buffer, 0, 100);
    qsort( str, size, sizeof( str[0] ), compare );
    setvbuf(fp, buffer, _IOFBF, 1024);

    while ( !isFinished ) {
        int i;
        printf("%s \n", str);
        fprintf(fp, "%s\n", str);

        for ( i = size - 2; i >= 0; --i )
            if (str[i] < str[i+1]) {
                break;
            }

        if ( i == -1 ) {
            isFinished = 1;
        } else {
            int ceilIndex = findCeil( str, str[i], i + 1, size - 1 );
            swap( &str[i], &str[ceilIndex] );
            qsort( str + i + 1, size - i - 1, sizeof(str[0]), compare );
        }   
    }
    fclose(fp);
}

int main() {
    char str[] = "ABCD";
    sortedPermutations( str );  
    return 0;
}

setvbuf 用于设置自定义缓冲区。例如，它用于设置大缓冲区并直接访问它。仅当缓冲区已满、或者刷新或关闭文件时，fprintf 才会打印到文件。而且您还使用 _IONBF 这意味着流根本不被缓冲。

所以 - 它只能工作，因为它没有缓冲，当您发送缓冲区 [100]，然后尝试打印 1024 时。因此还将缓冲区大小更改为 1024 并使用 _IOFBF。