confstr()

Get configuration-defined string values

Synopsis:

#include <unistd.h>

size_t confstr( int name, 
                char * buf,
                size_t len );

The confstr() functions lets applications get or set configuration-defined string values. This is similar to the sysconf() function, but is used where string values, rather than numeric values are returned. By default, the function queries and returns values in the system.

The name argument represents the system variable to query. The values are defined in <confname.h>; at least the following name values are valid:

Value	Description
_CS_ARCHITECTURE	The name of the instruction set architecture for this node's CPU(s).
_CS_DOMAIN	The domain name.
_CS_HOSTNAME	The name of this node in the network.
_CS_HW_PROVIDER	The name of the hardware manufacturer.
_CS_HW_SERIAL	Serial number associated with the hardware.
_CS_LIBPATH	A value similar to the LD_LIBRARY_PATH environment variable that finds all standard libraries.
_CS_MACHINE	This node's hardware type.
_CS_PATH	A value similar to the PATH environment variable that finds all standard utilities.
_CS_RELEASE	The current QNX OS release level.
_CS_RESOLVE	The contents of the `resolv.conf` file excluding the domain name.
_CS_SRPC_DOMAIN	The secure RPC domain.
_CS_SYSNAME	The operating system name.
_CS_TIMEZONE	Timezone string (TZ style)
_CS_VERSION	The current QNX OS version number.

The configuration-defined value is returned in the buffer pointed to by buf, and will be <= len bytes long, including the terminating NULL.

To find out the length of a configuration-defined value, call confstr() with buf set to NULL and len set to 0.

To set a configuration value:

OR your value to be defined (i.e. _CS_HOSTNAME) to _CS_SET
put this value in a NULL-terminated string
Set the value of len to 0

Returns:

A nonzero value (if a "get" is done, the value is the length of the configuration-defined value), or 0 if an error occurs (errno is set).

You can compare the confstr() return value against len to see if the configuration-defined value was truncated when retrieving a value, (this can't be done when setting a value).

Errors:

EINVAL: The name argument isn't a valid configuration-defined value.

Examples:

Print information similar to that returned by the uname() function:

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

#define BUFF_SIZE (256 + 1)

int main( void )
{
    char buff[BUFF_SIZE];

    if( confstr( _CS_SYSNAME, buff, BUFF_SIZE ) > 0 ) {
        printf( "System name: %s\n", buff );
    }
    
    if( confstr( _CS_HOSTNAME, buff, BUFF_SIZE ) > 0 ) {
        printf( "Host name: %s\n", buff );
    }
    
    if( confstr( _CS_RELEASE, buff, BUFF_SIZE ) > 0 ) {
        printf( "Release: %s\n", buff );
    }
    
    if( confstr( _CS_VERSION, buff, BUFF_SIZE ) > 0 ) {
        printf( "Version: %s\n", buff );
    }
    
    if( confstr( _CS_MACHINE, buff, BUFF_SIZE ) > 0 ) {
        printf( "Machine: %s\n", buff );
    }

    if( confstr( _CS_SET | _CS_HOSTNAME, "myhostname", 0 ) != 0 ) {
        printf( "Hostname set to: %s\n", "myhostname" );
    }

    return 0;
}

Classification:

POSIX 1003.1a

Safety:
Cancellation point	No
Interrupt handler	Yes
Signal handler	Yes
Thread	Yes

Caveats:

The confstr() function is part of a draft standard; its interface and/or behavior may change in the future.