PRB: fscanf() Fails to Read Consecutive Lines

• The C Run-time (CRT) included with: - Microsoft C for MS-DOS, versions 5.1, 6.0, 6.0a, 6.0ax - Microsoft C/C++ for MS-DOS, version 7.0 - Microsoft Visual C++ for Windows, versions 1.0, 1.5 - Microsoft Visual C++ 32-bit Edition, versions 1.0, 2.0, 2.1, 4.0, 4.1,

       4.2, 5.0
  

SYMPTOMS

When a file is open in text mode, an attempt to read lines of text with the fscanf() function may fail and only one line of text is read from the file.

CAUSE

The delimeter is set to "[^\n]". The fscanf() function reads up to but does not include the delimiting character. Therefore, the file stream stops at the first '\n' in the file. Subsequent fscanf() calls fail because the file pointer remains at the delimiting character and fscanf() cannot advance the function pointer past it.

RESOLUTION

Use one of the following two methods to move the file pointer past the delimiting character:

• Update the code to use the following fscanf() call:

        fscanf(stream, "%[^\n]%*c", line)
  

  The "%*c" format specifier reads one character from the input stream but does not assign it to any of the parameters in the fscanf function call.

• Call fgetc() after the fscanf() call to move the file pointer beyond the '\n' character.

MORE INFORMATION

The following code demonstrates this problem. It should read and print lines from a text file until it reaches EOF. However, it reads only the first line from the file. Since the end of file character has not been found, the example shown below will run in an infinite loop if the file stream contains a "\n" character.

Sample Code

   FILE *stream;
   char line[80];

   while ((fscanf(stream, "%[^\n]", line)) != EOF )
   {
      printf("Line = %s \n",line);
   }

   FILE *stream;
   char line[80];

   while ((fscanf(stream, "%[^\n]", line)) != EOF)
   {
      fgetc(stream);    // Reads in '\n' character and moves file
                        // stream past delimiting character
      printf("Line = %s \n", line);
   }