confstr()

Get configuration-defined string values

Synopsis:

#include <unistd.h>

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

Arguments:

name: The system variable to query; see below.
buf: A pointer to a buffer in which the function can store the value of the system variable.
len: The length of the buffer, in bytes.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The confstr() function lets applications get or (as a QNX Neutrino extension) set configuration-defined string values. This is similar to the sysconf() function, but you use it to get string values, rather than numeric values. By default, the function queries and returns values in the system.

Note: In order to set a configuration string, your process must have the PROCMGR_AID_CONFSET ability enabled (see procmgr_ability() for more information) and your code must follow the steps given in “Setting configuration values” below.

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

_CS_ARCHITECTURE: The name of the instruction set architecture for this node's CPU(s).
_CS_CONFIG_PATH: A colon-separated list of directories to search for configuration files.
_CS_DOMAIN: The domain name.
_CS_GRAPHICS: The graphics redirection.
_CS_HOSTNAME: The name of this node in the network.
Note: A hostname can consist only of letters, numbers, and hyphens, and must not start or end with a hyphen. For more information, see RFC 952.
_CS_HW_PROVIDER: The name of the hardware manufacturer.
_CS_HW_SERIAL: The serial number associated with the hardware.
_CS_LIBPATH: A value similar to the LD_LIBRARY_PATH environment variable that finds all standard libraries.
_CS_LOCALE: The name of the current locale.
_CS_MACHINE: This node's hardware type.
_CS_PAMCONF: The search path for PAM configuration files.
_CS_PAMLIB: The search path for PAM modules.
_CS_PATH: A value similar to the PATH environment variable that finds all standard utilities.
_CS_RELEASE: The current 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: The time zone string (TZ style).
_CS_V7_ENV: A space-separated list of environment variables that must be set for the QNX Neutrino to operate in a POSIX-conformant manner. For example, if this string contains POSIXLY_CORRECT, then your system will act in a POSIX-conformant manner if the POSIXLY_CORRECT environment variable is set.
_CS_VERSION: The current OS version number.

The configuration-defined value is returned in the buffer pointed to by buf, and will be less than or equal to len bytes long, including the terminating NULL. If the value, including the terminating NULL, is greater than len bytes long, it's truncated to len - 1 bytes and terminated with a NULL character.

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

Setting configuration values

As a QNX Neutrino extension, you can set a configuration value, as follows:

OR the name of the value (e.g., _CS_HOSTNAME) with _CS_SET.
Put the new value in a NULL-terminated string.
Set the value of len to 0.

For convenience, <confname.h> defines name values specifically for setting certain system variables, saving you from manually performing the first step listed above. These values include:

_CS_SET_DOMAIN
_CS_SET_RESOLVE
_CS_SET_TIMEZONE
_CS_SET_LOCALE
_CS_SET_GRAPHICS

Returns:

If you're getting the value:

If name has a configuration-defined value, confstr() returns the size of buffer that would be needed to hold the entire value, including the terminating null. If this size is greater than len, the string returned in buf is truncated.
If name is invalid, confstr() returns 0 and sets errno to indicate the error.
If name doesn't have a configuration-defined value, confstr() returns 0 and leaves errno unchanged.

If you're setting a value and an error occurs, confstr() returns 0 and sets errno. Any other value indicates success.

Errors:

EINVAL: The name argument isn't a valid configuration-defined value.
EPERM: The calling process doesn't have the required permission; see procmgr_ability().

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 1003.1

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