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std:: fwide

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< cpp ‎ | io ‎ | c
C++
Input/output library
C-style I/O
定义于头文件 <cwchar>
int fwide ( std:: FILE * stream, int mode ) ;

如果 mode > 0 ，则尝试使 stream 成为宽面向。如果 mode < 0 ，则尝试使 stream 成为字节面向。如果 mode == 0 ，则仅查询流的当前面向模式。

如果流的定向已经确定（通过执行输出操作或先前调用 fwide），此函数不执行任何操作。

目录

参数

stream - 指向待修改或查询的C I/O流的指针
mode - 整数值：大于零时设置流为宽模式，小于零时设置流为窄模式，等于零时仅进行查询

返回值

若调用后流为宽定向则返回大于零的整数，若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 '#'

参见

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C 文档 关于 fwide