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テキスト ファイルからテキストを 1 行ずつ読み取り、これらの行に対して何らかの処理を行いたいと考えています。私はすべての処理を実行できますが、malloc-realloc でメモリを拡張することはできません。テキストファイルの行文字がこの制限内であれば、すべて問題ありません。1行あたり10,000文字のような大きなファイルを使用すると、制限までしか読み取れません。の使い方がよくわかりませんrealloc()。このコードについて何ができますか?

 void stat(char* fileptr)
{

  FILE *fp;
  char *linebuffer;
  int line=0;
  int sum=0;
  int max=0;
  int min=0;
  int maxlinelen=512;
  int i=0,j=0;
  int maxlen=512;
  int curlinelen[maxlen];

  linebuffer=(char*) malloc(maxlinelen * sizeof(char));
  if(linebuffer==NULL)
    {
      printf("Error occurred allocating memory for linebuffer");
      exit(1);
    }


  if((fp=fopen(fileptr,"r"))!=NULL)
  {
    while((fgets(linebuffer,maxlinelen,fp))!=NULL)
      {
    if(strlen(linebuffer)==maxlinelen)
      {
        maxlinelen*=2;
        linebuffer=realloc(linebuffer,maxlinelen * sizeof(char));
        if(linebuffer==NULL)
          {
        printf("Error occurred reallocating space for linebuffer");
        exit(1);
          }
      }
    line++;

        sum=sum+strlen(linebuffer);
    curlinelen[i]=strlen(linebuffer);
    i++;

      }
  }
  min=curlinelen[0];
  max=curlinelen[0];
  for(j=0;j<line;j++)
    {
      if(curlinelen[j]<min)
    {
      min=curlinelen[j];
    }
      if(curlinelen[j]>max)
    {
      max=curlinelen[j];
    }
    }


 printf("No. of lines        =%d\n",line);
 printf("Maximum line length =%d\n",max);
 printf("Minimum line length =%d\n",min);       
 printf("Average line length =%8.2f\n",(float)sum/(float)line);

 fclose(fp);
}
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1 に答える 1

3 
fgets(linebuffer,maxlinelen,fp)

reads and stores at most maxlinelen - 1 characters in linebuffer and 0-terminates it. Thus

if(strlen(linebuffer)==maxlinelen)

is never satisfied, strlen(linebuffer) can be at most maxlinelen - 1. Change the condition, and you will see that maxlinelen increases if the file contains long lines (unless realloc fails).

Your current code will however count the partial line read in as an entire line then, and read the next chunk of the line as a new line. To grow the buffer until the entire line fits in, you must continue reading from the file before collecting the line length and incrementing the line count. But we must check whether a full line (including the newline at the end) was read in case fgets reads the maximal allowed number of chars before enlarging the buffer, or we'd concatenate the following line and count two (or in freak cases even more) lines as one.

while((fgets(linebuffer,maxlinelen,fp))!=NULL)
  {
  while((strlen(linebuffer) == maxlinelen-1) && (linebuffer[maxlinelen-2] != '\n'))
  {
    maxlinelen*=2;
    linebuffer=realloc(linebuffer,maxlinelen * sizeof(char));
    if(linebuffer==NULL)
    {
        printf("Error occurred reallocating space for linebuffer");
        exit(1);
    }
    fgets(linebuffer + (maxlinelen/2 - 1), maxlinelen/2 + 1, fp);
  }

would be a (rather inefficient, due to the strlen calls) way to do that.

于 2012-11-12T15:55:13.347 に答える