(libc.info.gz) String Parameters

Info Catalog

(libc.info.gz) Utility Minimums

(libc.info.gz) System Configuration

 
 31.12 String-Valued Parameters
 ==============================
 
 POSIX.2 defines a way to get string-valued parameters from the operating
 system with the function `confstr':
 
  -- Function: size_t confstr (int PARAMETER, char *BUF, size_t LEN)
      This function reads the value of a string-valued system parameter,
      storing the string into LEN bytes of memory space starting at BUF.
      The PARAMETER argument should be one of the `_CS_' symbols listed
      below.
 
      The normal return value from `confstr' is the length of the string
      value that you asked for.  If you supply a null pointer for BUF,
      then `confstr' does not try to store the string; it just returns
      its length.  A value of `0' indicates an error.
 
      If the string you asked for is too long for the buffer (that is,
      longer than `LEN - 1'), then `confstr' stores just that much
      (leaving room for the terminating null character).  You can tell
      that this has happened because `confstr' returns a value greater
      than or equal to LEN.
 
      The following `errno' error conditions are defined for this
      function:
 
     `EINVAL'
           The value of the PARAMETER is invalid.
 
    Currently there is just one parameter you can read with `confstr':
 
 `_CS_PATH'
      This parameter's value is the recommended default path for
      searching for executable files.  This is the path that a user has
      by default just after logging in.
 
 `_CS_LFS_CFLAGS'
      The returned string specifies which additional flags must be given
      to the C compiler if a source is compiled using the
      `_LARGEFILE_SOURCE' feature select macro;  Feature Test
      Macros.
 
 `_CS_LFS_LDFLAGS'
      The returned string specifies which additional flags must be given
      to the linker if a source is compiled using the
      `_LARGEFILE_SOURCE' feature select macro;  Feature Test
      Macros.
 
 `_CS_LFS_LIBS'
      The returned string specifies which additional libraries must be
      linked to the application if a source is compiled using the
      `_LARGEFILE_SOURCE' feature select macro;  Feature Test
      Macros.
 
 `_CS_LFS_LINTFLAGS'
      The returned string specifies which additional flags must be given
      to the lint tool if a source is compiled using the
      `_LARGEFILE_SOURCE' feature select macro;  Feature Test
      Macros.
 
 `_CS_LFS64_CFLAGS'
      The returned string specifies which additional flags must be given
      to the C compiler if a source is compiled using the
      `_LARGEFILE64_SOURCE' feature select macro;  Feature Test
      Macros.
 
 `_CS_LFS64_LDFLAGS'
      The returned string specifies which additional flags must be given
      to the linker if a source is compiled using the
      `_LARGEFILE64_SOURCE' feature select macro;  Feature Test
      Macros.
 
 `_CS_LFS64_LIBS'
      The returned string specifies which additional libraries must be
      linked to the application if a source is compiled using the
      `_LARGEFILE64_SOURCE' feature select macro;  Feature Test
      Macros.
 
 `_CS_LFS64_LINTFLAGS'
      The returned string specifies which additional flags must be given
      to the lint tool if a source is compiled using the
      `_LARGEFILE64_SOURCE' feature select macro;  Feature Test
      Macros.
 
    The way to use `confstr' without any arbitrary limit on string size
 is to call it twice: first call it to get the length, allocate the
 buffer accordingly, and then call `confstr' again to fill the buffer,
 like this:
 
      char *
      get_default_path (void)
      {
        size_t len = confstr (_CS_PATH, NULL, 0);
        char *buffer = (char *) xmalloc (len);
 
        if (confstr (_CS_PATH, buf, len + 1) == 0)
          {
            free (buffer);
            return NULL;
          }
 
        return buffer;
      }
 

Info Catalog

(libc.info.gz) Utility Minimums

(libc.info.gz) System Configuration