confstr() - get string-valued configurable variables
#include <unistd.h>
size_t confstr (int name, char *buf, size_t len)
The confstr(3) function provides a method for applications to get configuration defined string values.
The name argument specifies the system variable to be queried. Symbolic constants for each name value are found in the include file <unistd.h>. The len argument specifies the size of the buffer referenced by the argument buf. If len is non-zero, buf is a non-null pointer, and name has a value, up to len - 1 bytes of the value are copied into the buffer buf. The copied value is always null terminated.
The available values are as follows:
When the macros _ALL_SOURCE(1) or _XOPEN_SOURCE(1) are defined, or if _POSIX_C_SOURCE(1)==2, then these are also available:
If the call to confstr(3) is not successful, -1 is returned and errno is set appropriately. Otherwise, if the variable does not have a configuration defined value, 0 is returned and errno is not modified. Otherwise, the buffer size needed to hold the entire configuration-defined value is returned. If this size is greater than the argument len, the string in buf was truncated.
The confstr(3) function may fail and set error for any of the errors specified for the library function malloc(3).
In addition, the following errors may be reported: