Bug 5131 - getcwd(NULL,1024) does not behave as per man page
getcwd(NULL,1024) does not behave as per man page
Product: Red Hat Linux
Classification: Retired
Component: glibc (Show other bugs)
i386 Linux
medium Severity medium
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Assigned To: Cristian Gafton
Depends On:
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Reported: 1999-09-14 12:40 EDT by cosmo
Modified: 2008-05-01 11:37 EDT (History)
0 users

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Fixed In Version:
Doc Type: Bug Fix
Doc Text:
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Last Closed: 1999-10-06 13:12:17 EDT
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Description cosmo 1999-09-14 12:40:16 EDT
When called with a NULL buffer and a positive size argument
the man page states that a buffer of size bytes is
This does not apear true as appending to the end of the
buffer causes a SEGV when later malloc/free calls are made:

#include <unistd.h>
#include <stdlib.h>

main (int argc, char *argv[])
  char *cwd;
  char *chunk;
  size_t buffsize = 1024;
  size_t bigbuffsize = 10000;

  if ((cwd = getcwd(NULL, buffsize)) == NULL)
    printf ("getcwd (NULL, %d) == NULL\n");
    exit (1);
    printf ("cwd: %s\n", cwd);

  strcat (cwd, ":This is a bogus string");

  printf ("Now my buffer contains \"%s\"[%d]\n",
          cwd, strlen(cwd));

  if ((chunk = malloc (10000)) == NULL)
    printf ("malloc(%d) failure!\n", bigbuffsize);
    printf ("Grabbed %d bytes\n", bigbuffsize);
    free (chunk);

  if (cwd)
    free (cwd);

  return (0);
Comment 1 Cristian Gafton 1999-10-06 13:12:59 EDT
This function behaves as defined by the Single Unix Specification
version 2. We will have to fix the man page for it, but the behavior
is according to the specs:

The getcwd() function places an absolute pathname of the current
working directory in the array
pointed to by buf, and returns buf. The size argument is the size in
bytes of the character array
pointed to by the buf argument. If buf is a null pointer, the
behaviour of getcwd() is undefined.

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