gdb.info: The Print Command with Objective-C

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The Print Command With Objective-C

The print command has also been extended to accept methods.  For
example:
     print -[OBJECT hash]
will tell GDB to send the `hash' message to OBJECT and print the
result.  Also, an additional command has been added, `print-object' or
`po' for short, which is meant to print the description of an object.
However, this command may only work with certain Objective-C libraries
that have a particular hook function, `_NSPrintForDebugger', defined.