pathconf()--Get Configurable Path Name Variables

 #include <unistd.h>

 long pathconf(const char *path, int name);  

The pathconf() function lets an application determine the value of a configuration variable (name) associated with a particular file or directory (path).

If the named file is a symbolic link, pathconf() resolves the symbolic link.

Parameters

path

(Input) A pointer to the null-terminated path name of the file for which the value of the configuration variable is requested.

This parameter is assumed to be represented in the CCSID (coded character set identifier) currently in effect for the process. If the CCSID of the job is 65535, this parameter is assumed to be represented in the default CCSID of the job.

See QlgPathconf()--Get Configurable Path Name Variables for a description and an example of supplying the path in any CCSID.

name

(Input) The name of the configuration variable value requested.

The value of name can be any one of the following set of symbols defined in the <unistd.h> header file, each standing for a configuration variable:

_PC_LINK_MAX

Represents LINK_MAX, which indicates the maximum number of links the file can have. If path is a directory, pathconf() returns the maximum number of links that can be established to the directory itself.

_PC_MAX_CANON

Represents MAX_CANON, which indicates the maximum number of bytes in a terminal canonical input line.

_PC_MAX_INPUT

Represents MAX_INPUT, which indicates the minimum number of bytes for which space is available in a terminal input queue. This available space is the maximum number of bytes that a portable application can have the user enter before the application actually reads the input.

_PC_NAME_MAX

Represents NAME_MAX, which indicates the maximum number of bytes in a file name (not including any terminating null at the end if the file name is stored as a string). This symbol refers only to the file name itself; that is, the last component of the path name of the file. pathconf() returns the maximum length of file names, even when the path does not refer to a directory.

This value is the number of bytes allowed in the file name if it were encoded in the CCSID of the job. If the CCSID is mixed, this number is an estimate and may be larger than the actual allowable maximum.

_PC_PATH_MAX

Represents PATH_MAX, which indicates the maximum number of bytes in a complete path name (not including any terminating null at the end if the path name is stored as a string). pathconf() returns the maximum length of a relative path name relative to path, even when path does not refer to a directory.

This value is the number of bytes allowed in the path name if it were encoded in the CCSID of the job. If the CCSID is mixed, this number is an estimate and may be larger than the actual allowable maximum.

_PC_PIPE_BUF

Represents PIPE_BUF, which indicates the maximum number of bytes that can be written "atomically" to a pipe. If more than this number of bytes are written to a pipe, the operation may take more than one physical write operation and physical read operation to read the data on the other end of the pipe. If path is a FIFO special file, pathconf() returns the value for the file itself. If path is a directory, pathconf() returns the value for any FIFOs that exist or that can be created under the directory. If path is any other kind of file, an error of [EINVAL] is returned.

_PC_CHOWN_RESTRICTED

Represents _POSIX_CHOWN_RESTRICTED, as defined in the <unistd.h> header file. It restricts use of chown() to a job with appropriate privileges, and allows the group ID of a file to be changed only to the effective group ID of the job or to one of its supplementary group IDs. If path is a directory, pathconf() returns the value for any kind of file under the directory, but not for subdirectories of the directory.

_PC_NO_TRUNC

Represents _POSIX_NO_TRUNC, as defined in the <unistd.h> header file. It generates an error if a file name is longer than NAME_MAX. If path refers to a directory, the value returned by pathconf() applies to all files under that directory.

_PC_VDISABLE

Represents _POSIX_VDISABLE, as defined in the <unistd.h> header file. This symbol indicates that terminal special characters can be disabled using this character value, if it is defined.

_PC_THREAD_SAFE

This symbol is used to determine if the object represented by path resides in a threadsafe file system. pathconf() returns the value 1 if the file system is threadsafe and 0 if the file system is not threadsafe. fpathconf() will never fail with error code [ENOTSAFE] when called with _PC_THREAD_SAFE.

Authorities

Note: Adopted authority is not used.

Authorization required for pathconf()

Return Value

value

pathconf() was successful. The value of the variable requested in name is returned.

-1

One of the following has occurred:

• A particular variable has no limit (for example, _PC_PATH_MAX). The errno global variable is not changed.
• pathconf() was not successful. The errno is set.

Error Conditions

If fpathconf() is not successful, errno usually indicates one of the following errors. Under some conditions, errno could indicate an error other than those listed here.

If interaction with a file server is required to access the object, errno could indicate one of the following errors:

Error Messages

The following messages may be sent from this function:

Usage Notes

1. When this function is called with any configuration variable name except _PC_THREAD_SAFE, the following usage note applies:
   
   
   • This function will fail with error code [ENOTSAFE] when all the following conditions are true:
     
     
     • Where multiple threads exist in the job.
       
     • The object on which this function is operating resides in a file system that is not threadsafe. Only the following file systems are threadsafe for this function:
       
       
       • "Root" (/)
       • QOpenSys
       • User-defined
       • QNTC
       • QSYS.LIB
       • Independent ASP QSYS.LIB
       • QOPT
       • Network File System
       • QFileSvr.400

Related Information

• The <unistd.h> file (see Header Files for UNIX^®-Type Functions)
  
• chown()--Change Owner and Group of File
  
• fpathconf()--Get Configurable Path Name Variables by Descriptor
  
• QlgPathconf()--Get Configurable Path Name Variables

Example

The following example determines the maximum number of bytes in a file name.

Note: By using the code examples, you agree to the terms of the Code license and disclaimer information.

#include <stdio.h>
#include <unistd.h>
#include <errno.h>

main() {
  long result;

  errno = 0;
  puts("examining NAME_MAX limit for root filesystem");
  if ((result = pathconf("/", _PC_NAME_MAX)) == -1)
    if (errno == 0)
      puts("There is no limit to NAME_MAX.");
    else perror("pathconf() error");
  else
    printf("NAME_MAX is %ld\n", result);
}

Output:

examining NAME_MAX limit for root filesystem
NAME_MAX is 255

[ Back to top | UNIX-Type APIs | APIs by category ]