std::fwide

 

C++

编译器支持

独立和托管

语言

标准库

标准库头文件

命名要求

特性测试宏 (C++20)

语言支持库

概念库 (C++20)

元编程库 (C++11)

诊断库

通用实用程序库

字符串库

容器库

迭代器库

范围库 (C++20)

算法库

数值库

本地化库

输入/输出库

文件系统库 (C++17)

正则表达式库 (C++11)

并发支持库 (C++11)

执行支持库 (C++26)

技术规范

符号索引

外部库

 

输入/输出库

I/O 操作符

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 无格式输入/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

 

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

如果 mode > 0，尝试使 stream 成为宽字符方向。如果 mode < 0，尝试使 stream 成为字节方向。如果 mode == 0，只查询流的当前方向。

如果流的方向已经确定（通过执行输出或之前对 fwide 的调用），则此函数不执行任何操作。

参数

stream	-	指向要修改或查询的 C I/O 流的指针
mode	-	大于零的整数值表示将流设置为宽字符方向，小于零表示将流设置为窄字节方向，零表示仅查询

返回值

如果流在此调用后为宽字符方向，则返回大于零的整数；如果流在此调用后为字节方向，则返回小于零的整数；如果流没有方向，则返回零。

示例

以下代码设置和重置流的方向。

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 '#'

另请参阅

fopen	打开文件 (函数)
C 文档 对于 fwide