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glibc/stdio-common/printf_buffer_as_file.h

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stdio-common: Introduce buffers for implementing printf These buffers will eventually be used instead of FILE * objects to implement printf functions. The multibyte buffer is struct __printf_buffer, the wide buffer is struct __wprintf_buffer. To enable writing type-generic code, the header files printf_buffer-char.h and printf_buffer-wchar_t.h define the Xprintf macro differently, enabling Xprintf (buffer) to stand for __printf_buffer and __wprintf_buffer as appropriate. For common cases, macros like Xprintf_buffer are provided as a more syntactically convenient shortcut. Buffer-specific flush callbacks are implemented with a switch statement instead of a function pointer, to avoid hardening issues similar to those of libio vtables. struct __printf_buffer_as_file is needed to support custom printf specifiers because the public interface for that requires passing a FILE *, which is why there is a trapdoor back from these buffers to FILE * streams. Since the immediate user of these interfaces knows when processing has finished, there is no flush callback for the end of processing, only a flush callback for the intermediate buffer flush. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
2022-12-19 17:56:54 +00:00
/* FILE * interface to a struct __*printf_buffer.
Update copyright dates with scripts/update-copyrights
2023-01-06 21:08:04 +00:00
Copyright (C) 2022-2023 Free Software Foundation, Inc.
stdio-common: Introduce buffers for implementing printf These buffers will eventually be used instead of FILE * objects to implement printf functions. The multibyte buffer is struct __printf_buffer, the wide buffer is struct __wprintf_buffer. To enable writing type-generic code, the header files printf_buffer-char.h and printf_buffer-wchar_t.h define the Xprintf macro differently, enabling Xprintf (buffer) to stand for __printf_buffer and __wprintf_buffer as appropriate. For common cases, macros like Xprintf_buffer are provided as a more syntactically convenient shortcut. Buffer-specific flush callbacks are implemented with a switch statement instead of a function pointer, to avoid hardening issues similar to those of libio vtables. struct __printf_buffer_as_file is needed to support custom printf specifiers because the public interface for that requires passing a FILE *, which is why there is a trapdoor back from these buffers to FILE * streams. Since the immediate user of these interfaces knows when processing has finished, there is no flush callback for the end of processing, only a flush callback for the intermediate buffer flush. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
2022-12-19 17:56:54 +00:00
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
/* Registered printf format specifier callbacks produce data via a
FILE * stream. struct __printf_buffer_as_file enables vfprintf to
create a suitable stdio stream. Likewise struct
__wprintf_buffer_as_file for vfwprintf. */
#ifndef PRINTF_BUFFER_AS_FILE_H
#define PRINTF_BUFFER_AS_FILE_H
#include <libio/libioP.h>
struct __printf_buffer;
struct __printf_buffer_as_file
{
/* Interface to libio. */
FILE stream;
const struct _IO_jump_t *vtable;
/* Pointer to the underlying buffer. */
struct __printf_buffer *next;
};
/* Initialization *FP so that data written to its FILE * stream ends
up in NEXT. */
void __printf_buffer_as_file_init (struct __printf_buffer_as_file *fp,
struct __printf_buffer *next)
attribute_hidden;
/* Returns the FILE * that can be used to write data to the
buffer. */
static inline FILE *
__printf_buffer_as_file_get (struct __printf_buffer_as_file *file)
{
return &file->stream;
}
/* Transfers all pending data from the FILE * to the underlying
buffer. Returns true if there have been no errors. */
bool __printf_buffer_as_file_terminate (struct __printf_buffer_as_file *)
attribute_hidden;
/* Wide variant follows. */
struct __wprintf_buffer;
struct __wprintf_buffer_as_file
{
/* Interface to libio. */
FILE stream;
const struct _IO_jump_t *vtable;
struct _IO_wide_data wide_stream;
/* Pointer to the underlying buffer. */
struct __wprintf_buffer *next;
};
void __wprintf_buffer_as_file_init (struct __wprintf_buffer_as_file *fp,
struct __wprintf_buffer *next)
attribute_hidden;
static inline FILE *
__wprintf_buffer_as_file_get (struct __wprintf_buffer_as_file *file)
{
return &file->stream;
}
bool __wprintf_buffer_as_file_terminate (struct __wprintf_buffer_as_file *)
attribute_hidden;
#endif /* PRINTF_BUFFER_AS_FILE_H */
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