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| <title>Using the GNU Compiler Collection (GCC): Deprecated Features</title> |
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| <a name="Deprecated-Features-1"></a> |
| <h3 class="section">7.12 Deprecated Features</h3> |
| |
| <p>In the past, the GNU C++ compiler was extended to experiment with new |
| features, at a time when the C++ language was still evolving. Now that |
| the C++ standard is complete, some of those features are superseded by |
| superior alternatives. Using the old features might cause a warning in |
| some cases that the feature will be dropped in the future. In other |
| cases, the feature might be gone already. |
| </p> |
| <p>While the list below is not exhaustive, it documents some of the options |
| that are now deprecated: |
| </p> |
| <dl compact="compact"> |
| <dt><code>-fexternal-templates</code></dt> |
| <dt><code>-falt-external-templates</code></dt> |
| <dd><p>These are two of the many ways for G++ to implement template |
| instantiation. See <a href="Template-Instantiation.html#Template-Instantiation">Template Instantiation</a>. The C++ standard clearly |
| defines how template definitions have to be organized across |
| implementation units. G++ has an implicit instantiation mechanism that |
| should work just fine for standard-conforming code. |
| </p> |
| </dd> |
| <dt><code>-fstrict-prototype</code></dt> |
| <dt><code>-fno-strict-prototype</code></dt> |
| <dd><p>Previously it was possible to use an empty prototype parameter list to |
| indicate an unspecified number of parameters (like C), rather than no |
| parameters, as C++ demands. This feature has been removed, except where |
| it is required for backwards compatibility. See <a href="Backwards-Compatibility.html#Backwards-Compatibility">Backwards Compatibility</a>. |
| </p></dd> |
| </dl> |
| |
| <p>G++ allows a virtual function returning ‘<samp>void *</samp>’ to be overridden |
| by one returning a different pointer type. This extension to the |
| covariant return type rules is now deprecated and will be removed from a |
| future version. |
| </p> |
| <p>The G++ minimum and maximum operators (‘<samp><?</samp>’ and ‘<samp>>?</samp>’) and |
| their compound forms (‘<samp><?=</samp>’) and ‘<samp>>?=</samp>’) have been deprecated |
| and are now removed from G++. Code using these operators should be |
| modified to use <code>std::min</code> and <code>std::max</code> instead. |
| </p> |
| <p>The named return value extension has been deprecated, and is now |
| removed from G++. |
| </p> |
| <p>The use of initializer lists with new expressions has been deprecated, |
| and is now removed from G++. |
| </p> |
| <p>Floating and complex non-type template parameters have been deprecated, |
| and are now removed from G++. |
| </p> |
| <p>The implicit typename extension has been deprecated and is now |
| removed from G++. |
| </p> |
| <p>The use of default arguments in function pointers, function typedefs |
| and other places where they are not permitted by the standard is |
| deprecated and will be removed from a future version of G++. |
| </p> |
| <p>G++ allows floating-point literals to appear in integral constant expressions, |
| e.g. ‘<samp> enum E { e = int(2.2 * 3.7) } </samp>’ |
| This extension is deprecated and will be removed from a future version. |
| </p> |
| <p>G++ allows static data members of const floating-point type to be declared |
| with an initializer in a class definition. The standard only allows |
| initializers for static members of const integral types and const |
| enumeration types so this extension has been deprecated and will be removed |
| from a future version. |
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