Question

I have written a function to wrap GNU getline() and remove the trailing newline, but for some reason it has no effect. Am I doing something wrong?

ssize_t readline(char **lineptr, FILE *stream)
{
  size_t len = 0;  // Size of the buffer, ignored.

  ssize_t chars = getline(lineptr, &len, stream);

  if((*lineptr)[chars] == '\n') {
    (*lineptr)[chars] = '\0';
    --chars;
  }

  return chars;
}

It compiles and links without problems, but the newline is not replaced with a null-terminator. I’ve verified the if() statement is running. Thanks for any help!

Answer 1

getline returns the number of characters read. So you have to use chars-1 rather than char.

if ((*lineptr)[chars - 1] == '\n') 
  {
      (*lineptr)[chars - 1] = '\0';
      --chars;
  }

man getline (3)

On success, getline() and getdelim() return the number of characters read, including the > delimiter character, but not
including the terminating null byte. This value can be used to handle
embedded null bytes in the line read.