前言
在 C++ 中有个扩展库 ext，里面有一些黑科技（hash, splay, binomial_heap 等等），
在 Windows 环境中，我们运行 Dev-C++ 并在头文件写 #include<bits/extc++.h> 时，经常会收到 [Error] iconv.h: No such file or directory 的编译报错。
所以为了代替他，我们会写很多
#include<ext/pb_ds/hash_policy.hpp>
#include<ext/pb_ds/assoc_container.hpp>
诸如此类。这不失为一个解决方案，但是万能头显然更加方便快捷。
现在我们来试着解决这个问题。
Step 1
找到您电脑上头文件的存储位置。通常为 C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include\c++。
如果找不到可以新建一个 cpp 文件，开头写上 #include<iostream> 然后 Ctrl+左键点一下就可以知道文件目录了。
Step 2
在此目录下新建一个 iconv.h 文件，把下列内容复制进去：
/* Copyright (C) 1999-2019 Free Software Foundation, Inc.
This file is part of the GNU LIBICONV Library.
The GNU LIBICONV Library is free software; you can redistribute it
and/or modify it under the terms of the GNU Library General Public
License as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
The GNU LIBICONV 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
Library General Public License for more details.
You should have received a copy of the GNU Library General Public
License along with the GNU LIBICONV Library; see the file COPYING.LIB.
If not, see <https://www.gnu.org/licenses/>. */
/* When installed, this file is called "iconv.h". */
#ifndef _LIBICONV_H
#define _LIBICONV_H
#define _LIBICONV_VERSION 0x0110 /* version number: (major<<8) + minor */
extern __declspec (dllimport) int _libiconv_version; /* Likewise */
/* We would like to #include any system header file which could define
iconv_t, 1. in order to eliminate the risk that the user gets compilation
errors because some other system header file includes /usr/include/iconv.h
which defines iconv_t or declares iconv after this file, 2. when compiling
for LIBICONV_PLUG, we need the proper iconv_t type in order to produce
binary compatible code.
But gcc's #include_next is not portable. Thus, once libiconv's iconv.h
has been installed in /usr/local/include, there is no way any more to
include the original /usr/include/iconv.h. We simply have to get away
without it.
Ad 1. The risk that a system header file does
#include "iconv.h" or #include_next "iconv.h"
is small. They all do #include <iconv.h>.
Ad 2. The iconv_t type is a pointer type in all cases I have seen. (It
has to be a scalar type because (iconv_t)(-1) is a possible return value
from iconv_open().) */
/* Define iconv_t ourselves. */
#undef iconv_t
#define iconv_t libiconv_t
typedef void* iconv_t;
/* Get size_t declaration.
Get wchar_t declaration if it exists. */
#include <stddef.h>
/* Get errno declaration and values. */
#include <errno.h>
/* Some systems, like SunOS 4, don't have EILSEQ. Some systems, like BSD/OS,
have EILSEQ in a different header. On these systems, define EILSEQ
ourselves. */
#ifndef EILSEQ
#define EILSEQ
#endif
#ifdef __cplusplus
extern "C" {
#endif
/* Allocates descriptor for code conversion from encoding ‘fromcode’ to
encoding ‘tocode’. */
#ifndef LIBICONV_PLUG
#define iconv_open libiconv_open
#endif
extern iconv_t iconv_open (const char* tocode, const char* fromcode);
/* Converts, using conversion descriptor ‘cd’, at most ‘*inbytesleft’ bytes
starting at ‘*inbuf’, writing at most ‘*outbytesleft’ bytes starting at
‘*outbuf’.
Decrements ‘*inbytesleft’ and increments ‘*inbuf’ by the same amount.
Decrements ‘*outbytesleft’ and increments ‘*outbuf’ by the same amount. */
#ifndef LIBICONV_PLUG
#define iconv libiconv
#endif
extern size_t iconv (iconv_t cd, char* * inbuf, size_t *inbytesleft, char* * outbuf, size_t *outbytesleft);
/* Frees resources allocated for conversion descriptor ‘cd’. */
#ifndef LIBICONV_PLUG
#define iconv_close libiconv_close
#endif
extern int iconv_close (iconv_t cd);
#ifdef __cplusplus
}
#endif
#ifndef LIBICONV_PLUG
/* Nonstandard extensions. */
#if 1
#if 0
/* Tru64 with Desktop Toolkit C has a bug: <stdio.h> must be included before
<wchar.h>.
BSD/OS 4.0.1 has a bug: <stddef.h>, <stdio.h> and <time.h> must be
included before <wchar.h>. */
#include <stddef.h>
#include <stdio.h>
#include <time.h>
#endif
#include <wchar.h>
#endif
#ifdef __cplusplus
extern "C" {
#endif
/* A type that holds all memory needed by a conversion descriptor.
A pointer to such an object can be used as an iconv_t. */
typedef struct {
void* dummy1[28];
#if 1
mbstate_t dummy2;
#endif
} iconv_allocation_t;
/* Allocates descriptor for code conversion from encoding ‘fromcode’ to
encoding ‘tocode’ into preallocated memory. Returns an error indicator
(0 or -1 with errno set). */
#define iconv_open_into libiconv_open_into
extern int iconv_open_into (const char* tocode, const char* fromcode,
iconv_allocation_t* resultp);
/* Control of attributes. */
#define iconvctl libiconvctl
extern int iconvctl (iconv_t cd, int request, void* argument);
/* Hook performed after every successful conversion of a Unicode character. */
typedef void (*iconv_unicode_char_hook) (unsigned int uc, void* data);
/* Hook performed after every successful conversion of a wide character. */
typedef void (*iconv_wide_char_hook) (wchar_t wc, void* data);
/* Set of hooks. */
struct iconv_hooks {
iconv_unicode_char_hook uc_hook;
iconv_wide_char_hook wc_hook;
void* data;
};
/* Fallback function. Invoked when a small number of bytes could not be
converted to a Unicode character. This function should process all
bytes from inbuf and may produce replacement Unicode characters by calling
the write_replacement callback repeatedly. */
typedef void (*iconv_unicode_mb_to_uc_fallback)
(const char* inbuf, size_t inbufsize,
void (*write_replacement) (const unsigned int *buf, size_t buflen,
void* callback_arg),
void* callback_arg,
void* data);
/* Fallback function. Invoked when a Unicode character could not be converted
to the target encoding. This function should process the character and
may produce replacement bytes (in the target encoding) by calling the
write_replacement callback repeatedly. */
typedef void (*iconv_unicode_uc_to_mb_fallback)
(unsigned int code,
void (*write_replacement) (const char *buf, size_t buflen,
void* callback_arg),
void* callback_arg,
void* data);
#if 1
/* Fallback function. Invoked when a number of bytes could not be converted to
a wide character. This function should process all bytes from inbuf and may
produce replacement wide characters by calling the write_replacement
callback repeatedly. */
typedef void (*iconv_wchar_mb_to_wc_fallback)
(const char* inbuf, size_t inbufsize,
void (*write_replacement) (const wchar_t *buf, size_t buflen,
void* callback_arg),
void* callback_arg,
void* data);
/* Fallback function. Invoked when a wide character could not be converted to
the target encoding. This function should process the character and may
produce replacement bytes (in the target encoding) by calling the
write_replacement callback repeatedly. */
typedef void (*iconv_wchar_wc_to_mb_fallback)
(wchar_t code,
void (*write_replacement) (const char *buf, size_t buflen,
void* callback_arg),
void* callback_arg,
void* data);
#else
/* If the wchar_t type does not exist, these two fallback functions are never
invoked. Their argument list therefore does not matter. */
typedef void (*iconv_wchar_mb_to_wc_fallback) ();
typedef void (*iconv_wchar_wc_to_mb_fallback) ();
#endif
/* Set of fallbacks. */
struct iconv_fallbacks {
iconv_unicode_mb_to_uc_fallback mb_to_uc_fallback;
iconv_unicode_uc_to_mb_fallback uc_to_mb_fallback;
iconv_wchar_mb_to_wc_fallback mb_to_wc_fallback;
iconv_wchar_wc_to_mb_fallback wc_to_mb_fallback;
void* data;
};
/* Requests for iconvctl. */
#define ICONV_TRIVIALP 0 /* int *argument */
#define ICONV_GET_TRANSLITERATE 1 /* int *argument */
#define ICONV_SET_TRANSLITERATE 2 /* const int *argument */
#define ICONV_GET_DISCARD_ILSEQ 3 /* int *argument */
#define ICONV_SET_DISCARD_ILSEQ 4 /* const int *argument */
#define ICONV_SET_HOOKS 5 /* const struct iconv_hooks *argument */
#define ICONV_SET_FALLBACKS 6 /* const struct iconv_fallbacks *argument */
/* Listing of locale independent encodings. */
#define iconvlist libiconvlist
extern void iconvlist (int (*do_one) (unsigned int namescount,
const char * const * names,
void* data),
void* data);
/* Canonicalize an encoding name.
The result is either a canonical encoding name, or name itself. */
extern const char * iconv_canonicalize (const char * name);
/* Support for relocatable packages. */
/* Sets the original and the current installation prefix of the package.
Relocation simply replaces a pathname starting with the original prefix
by the corresponding pathname with the current prefix instead. Both
prefixes should be directory names without trailing slash (i.e. use ""
instead of "/"). */
extern void libiconv_set_relocation_prefix (const char *orig_prefix,
const char *curr_prefix);
#ifdef __cplusplus
}
#endif
#endif
#endif /* _LIBICONV_H */
Step 3
保存。再次编译时可以顺利通过。