std::fwide

 

C++

编译器支持

自由（freestanding）与宿主（hosted）

语言

标准库

标准库头文件

具名要求

特性测试宏 (C++20)

语言支持库

概念库 (C++20)

诊断库

内存管理库

元编程库 (C++11)

通用工具库

容器库

迭代器库

范围库 (C++20)

算法库

字符串库

文本处理库

数值库

日期和时间库

输入/输出库

文件系统库 (C++17)

并发支持库 (C++11)

执行控制库 (C++26)

技术规范

符号索引

外部库

 

输入/输出库

I/O 操纵器

打印函数 (C++23)

C 风格 I/O

缓冲区

basic_streambuf

basic_filebuf

basic_stringbuf

basic_spanbuf (C++23)

strstreambuf (C++98/26*)

basic_syncbuf (C++20)

流

抽象

ios_base

basic_ios

basic_istream

basic_ostream

basic_iostream

文件 I/O

basic_ifstream

basic_ofstream

basic_fstream

字符串 I/O

basic_istringstream

basic_ostringstream

basic_stringstream

数组 I/O

basic_ispanstream (C++23)

basic_ospanstream (C++23)

basic_spanstream (C++23)

istrstream (C++98/26*)

ostrstream (C++98/26*)

strstream (C++98/26*)

同步输出

basic_osyncstream (C++20)

类型

streamoff

streamsize

fpos

错误类别接口

iostream_category (C++11)

io_errc (C++11)

 

C 风格 I/O

类型和对象
FILE fpos_t	stdinstdoutstderr
函数
文件访问 fopen freopen fclose fflush fwide setbuf setvbuf 直接输入/输出 fread fwrite 非格式化输入/输出 fgetcgetc fgets fputcputc fputs getchar gets (直到 C++14) putchar puts ungetc fgetwcgetwc fgetws fputwcputwc fputws getwchar putwchar ungetwc 格式化输入 scanffscanfsscanf vscanfvfscanfvsscanf (C++11)(C++11)(C++11)     wscanffwscanfswscanf vwscanfvfwscanfvswscanf (C++11)(C++11)(C++11)	格式化输出 printffprintfsprintfsnprintf (C++11) vprintfvfprintfvsprintfvsnprintf (C++11)     wprintffwprintfswprintf vwprintfvfwprintfvswprintf 文件定位 ftell fgetpos fseek fsetpos rewind 错误处理 clearerr feof ferror perror 文件操作 remove rename tmpfile tmpnam

 

在头文件 <cwchar> 中定义
int fwide( std::FILE* stream, int mode );

若 mode > 0，尝试令 stream 为宽定向。若 mode < 0，尝试令 stream 为字节定向。若 mode == 0，则只查询流的当前定向。

若流的定向已由（通过执行输出或早先调用 fwide）决定，则此函数不做任何事。

参数

stream	-	指向 C I/O 流的指针，以修改或查询
mode	-	整数值，大于零以设置流为宽定向，小于零以设置流为窄定向，或零以只查询

返回值

若此调用后流为宽定向则返回大于零的整数，若此调用后流为字节定向则返回小于零的整数，若流无定向则返回零。

示例

以下代码设置并重置流的定向。

运行此代码

#include <cstdio>
#include <cstdlib>
#include <cwchar>
#include <iostream>
 
void show_orientation(int n)
{
    n < 0 ? std::wcout << "\tnarrow orientation\n" :
    n > 0 ? std::wcout << "\twide orientation\n" :
            std::wcout << "\tno orientation\n";
}
 
void try_read(FILE* fp)
{
    if (const int c = std::fgetc(fp); c == EOF)
        std::wcout << "\tnarrow character read failed\n";
    else
        std::wcout << "\tnarrow character read '" << static_cast<char>(c) << "'\n";
 
    if (const wint_t wc = std::fgetwc(fp); wc == WEOF)
        std::wcout << "\twide character read failed\n";
    else
        std::wcout << "\twide character read '" << static_cast<wchar_t>(wc) << "'\n";
}
 
int main()
{
    enum fwide_orientation : int { narrow = -1, query, wide };
 
    FILE* fp = std::fopen("main.cpp", "r");
    if (!fp)
    {
        std::wcerr << "fopen() failed\n";
        return EXIT_FAILURE;
    }
 
    std::wcout << "1) A newly opened stream has no orientation.\n";
    show_orientation(std::fwide(fp, fwide_orientation::query));
 
    std::wcout << "2) Establish byte orientation.\n";
    show_orientation(std::fwide(fp, fwide_orientation::narrow));
    try_read(fp);
 
    std::wcout << "3) Only freopen() can reset stream orientation.\n";
    if (std::freopen("main.cpp", "r", fp) == NULL)
    {
        std::wcerr << "freopen() failed\n";
        return EXIT_FAILURE;
    }
 
    std::wcout << "4) A reopened stream has no orientation.\n";
    show_orientation(std::fwide(fp, fwide_orientation::query));
 
    std::wcout << "5) Establish wide orientation.\n";
    show_orientation(std::fwide(fp, fwide_orientation::wide));
    try_read(fp);
 
    std::fclose(fp);
}

可能的输出

1) A newly opened stream has no orientation.
        no orientation
2) Establish byte orientation.
        narrow orientation
        narrow character read '#'
        wide character read failed
3) Only freopen() can reset stream orientation.
4) A reopened stream has no orientation.
        no orientation
5) Establish wide orientation.
        wide orientation
        narrow character read failed
        wide character read '#'

参阅

fopen	打开文件 (函数)
C 文档 关于 fwide