NAME

confstr - get configurable variables

 SYNOPSIS

#include <unistd.h>

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

 DESCRIPTION

The confstr() function provides a method for applications to get configuration-defined string values. Its use and purpose are similar to sysconf(), but it is used where string values rather than numeric values are returned.

The name argument represents the system variable to be queried. The implementation supports the following name values, defined in <unistd.h>. It may support others:

_CS_PATH
_CS_XBS5_ILP32_OFF32_CFLAGS
_CS_XBS5_ILP32_OFF32_LDFLAGS
_CS_XBS5_ILP32_OFF32_LIBS
_CS_XBS5_ILP32_OFF32_LINTFLAGS
_CS_XBS5_ILP32_OFFBIG_CFLAGS
_CS_XBS5_ILP32_OFFBIG_LDFLAGS
_CS_XBS5_ILP32_OFFBIG_LIBS
_CS_XBS5_ILP32_OFFBIG_LINTFLAGS
_CS_XBS5_LP64_OFF64_CFLAGS
_CS_XBS5_LP64_OFF64_LDFLAGS
_CS_XBS5_LP64_OFF64_LIBS
_CS_XBS5_LP64_OFF64_LINTFLAGS
_CS_XBS5_LPBIG_OFFBIG_CFLAGS
_CS_XBS5_LPBIG_OFFBIG_LDFLAGS
_CS_XBS5_LPBIG_OFFBIG_LIBS
_CS_XBS5_LPBIG_OFFBIG_LINTFLAGS

If len is not 0, and if name has a configuration-defined value, confstr() copies that value into the len-byte buffer pointed to by buf. If the string to be returned is longer than len bytes, including the terminating null, then confstr() truncates the string to len-1 bytes and null-terminates the result. The application can detect that the string was truncated by comparing the value returned by confstr() with len.

If len is 0 and buf is a null pointer, then confstr() still returns the integer value as defined below, but does not return a string. If len is 0 but buf is not a null pointer, the result is unspecified.

 RETURN VALUE

If name has a configuration-defined value, confstr() returns the size of buffer that would be needed to hold the entire configuration-defined value including the terminating null. If this return value 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 does not have a configuration-defined value, confstr() returns 0 and leaves errno unchanged.

 ERRORS

The confstr() function will fail if:

[EINVAL]

The value of the name argument is invalid.

 EXAMPLES

None.

 APPLICATION USAGE

An application can distinguish between an invalid name parameter value and one that corresponds to a configurable variable that has no configuration-defined value by checking if errno is modified. This mirrors the behaviour of sysconf().

The original need for this function was to provide a way of finding the configuration-defined default value for the environment variable PATH. Since PATH can be modified by the user to include directories that could contain utilities replacing XCU specification standard utilities, applications need a way to determine the system-supplied PATH environment variable value that contains the correct search path for the standard utilities.

An application could use:

confstr(name, (char *)NULL, (size_t)0)

to find out how big a buffer is needed for the string value; use malloc() to allocate a buffer to hold the string; and call confstr() again to get the string. Alternately, it could allocate a fixed, static buffer that is big enough to hold most answers (perhaps 512 or 1024 bytes), but then use malloc() to allocate a larger buffer if it finds that this is too small.

 FUTURE DIRECTIONS

None.

 SEE ALSO

pathconf(), sysconf(), <unistd.h>, the XCU specification of getconf.

DERIVATION

Derived from the ISO POSIX-2 standard.