11.6. Summary

SUSv3 specifies limits that an implementation may enforce and system options that an implementation may support.

Often, it is desirable not to hard-code assumptions about system limits and options into a program, since these may vary across implementations and also on a single implementation, either at run time or across file systems. Therefore, SUSv3 specifies methods by which an implementation can advertise the limits and options it supports. For most limits, SUSv3 specifies a minimum value that all implementations must support. Additionally, each implementation can advertise its implementation-specific limits and options at compile time (via a constant definition in <limits.h> or <unistd.h>) and/or run time (via a call to sysconf(), pathconf(), or fpathconf()). These techniques may similarly be used to find out which SUSv3 options an implementation supports. In some cases, it may not be possible to determine a particular limit using either of these methods. For such indeterminate limits, we must resort to ad hoc techniques to determine the limit to which an application should adhere.