Template instantiation

The compiler does all template instantiations automatically, and makes sure there is only one definition of each template entity left after linking. The compiler does this by emitting template entities in named common sections. Therefore, all duplicate common sections, that is, common sections with the same name, are eliminated by the linker.

Note

You can limit the number of concurrent instantiations of a given template with the --pending_instantiations compiler option.

See also ‑‑pending_instantiations=n for more information.

Show/hideImplicit inclusion

When implicit inclusion is enabled, the compiler assumes that if it requires a definition to instantiate a template entity declared in a .h file it can implicitly include the corresponding .cc file to get the source code for the definition. For example, if a template entity ABC::f is declared in file xyz.h, and an instantiation of ABC::f is required in a compilation but no definition of ABC::f appears in the source code processed by the compilation, then the compiler checks to see if a file xyz.cc exists. If this file exists, the compiler processes the file as if it were included at the end of the main source file.

To find the template definition file for a given template entity the compiler has to know the full path name of the file where the template is declared and whether the file is included using the system include syntax, for example, #include <file.h>. This information is not available for preprocessed source containing #line directives. Consequently, the compiler does not attempt implicit inclusion for source code containing #line directives.

The compiler looks for the definition-file suffixes .cc and .CC.

You can turn implicit inclusion mode on or off with the command-line options --implicit_include and --no_implicit_include.

Implicit inclusions are only performed during the normal compilation of a file, that is, when not using the -E command-line option.

See Compiler Command-line Options for more information.

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