-qoldpassbyvalue (C++ only)

Pragma equivalent

#pragma pass_by_value

Purpose

Specifies how classes containing const or reference members are passed in function arguments.

The IBM® C++ Compiler V3.6 uses pass by value only if the class has no const or reference data members, and the copy constructor is trivial and the destructor is trivial. VisualAge® C++ V5.0 and later compilers use pass by value if the copy constructor is trivial and the destructor is trivial, regardless of const or reference data members. When -qoldpassbyvalue is in effect, the compiler uses the 3.6 behavior so that when a class containing a const or reference member is passed as a function argument, it is not passed by value. When -qnooldpassbyvalue is in effect, the compiler uses the new behavior so that when a class containing a const or reference member is passed as a function argument, it is passed by value.

The #pragma pass_by_value directive allows you greater control over this option for specific files or sections of source code.

Syntax


Option syntax

        .-nooldpassbyvalue-.   
>>- -q--+-oldpassbyvalue---+-----------------------------------><


>>-| Pragma syntax |-------------------------------------------><

Pragma syntax

|--#--pragma--pass_by_value--(--+-compat--+--)------------------|
                                +-ansi----+      
                                +-default-+      
                                +-source--+      
                                +-pop-----+      
                                '-reset---'

Defaults

-qnooldpassbyvalue

Parameters

compat (pragma only): Sets -qoldpassbyvalue for the code that follows it. This instructs the compiler to use the earlier behavior: when a class containing a const or reference member is passed as a function argument, it is not passed by value.
ansi | default (pragma only): Sets -qnooldpassbyvalue for the code that follows it. This instructs the compiler to use the new behavior: when a class containing a const or reference member is passed as a function argument, it is passed by value.
source (pragma only): Reverts to the setting specified by the command-line option; if no option has been specified, reverts to the default setting (-qnooldpassbyvalue).
pop | reset (pragma only): Discards the current pragma setting and reverts to the setting specified by the previous pragma directive. If no previous pragma was specified, reverts to the command-line or default option setting.

Usage

Use this option if you are linking to libraries compiled with IBM C++ Compiler V3.6 or earlier. Otherwise, functions that have const or reference class parameter types will give incorrect behavior when they are called from modules compiled with a later version of the compiler. Library headers compiled with IBM C++ Compiler V3.6 or earlier should be protected with the #pragma pass_by_value directive so that users of these libraries will get the correct calling convention for functions in those libraries that use class parameters.

Predefined macros

None.

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