# Extra Clang Tools 22.1.2 documentation

## clang-tidy - modernize-deprecated-headers

# modernize-deprecated-headers

Some headers from C library were deprecated in C++ and are no longer welcome in C++ codebases. Some have no effect in C++. For more details refer to the C++14 Standard [depr.c.headers] section.

This check replaces C standard library headers with their C++ alternatives and removes redundant ones.

    // C++ source file...
    #include <assert.h>
    #include <stdbool.h>

    // becomes

    #include <cassert>
    // No 'stdbool.h' here.

Important note: the Standard doesn’t guarantee that the C++ headers declare all the same functions in the global namespace. The check in its current form can break the code that uses library symbols from the global namespace.

- <assert.h>

- <complex.h>

- <ctype.h>

- <errno.h>

- <fenv.h> // deprecated since C++11

- <float.h>

- <inttypes.h>

- <limits.h>

- <locale.h>

- <math.h>

- <setjmp.h>

- <signal.h>

- <stdarg.h>

- <stddef.h>

- <stdint.h>

- <stdio.h>

- <stdlib.h>

- <string.h>

- <tgmath.h> // deprecated since C++11

- <time.h>

- <uchar.h> // deprecated since C++11

- <wchar.h>

- <wctype.h>

If the specified standard is older than C++11 the check will only replace headers deprecated before C++11, otherwise – every header that appeared in the previous list.

These headers don’t have effect in C++:

- <iso646.h>

- <stdalign.h>

- <stdbool.h>

The checker ignores include directives within extern “C” { … } blocks, since a library might want to expose some API for C and C++ libraries.

    // C++ source file...
    extern "C" {
    #include <assert.h>  // Left intact.
    #include <stdbool.h> // Left intact.
    }

## Options

CheckHeaderFile

  clang-tidy cannot know if the header file included by the currently analyzed C++ source file is not included by any other C source files. Hence, to omit false-positives and wrong fixit-hints, we ignore emitting reports into header files. One can set this option to true if they know that the header files in the project are only used by C++ source files. Default is false.