C style file input/output --- unformatted input/output

The CI/O subset of the C++ standard library implements C-style stream input/output operations. The <cstdio> header file provides general file support and provides functions with narrow and multibyte character input/output capabilities, while the <cwchar> header file provides functions with wide character input/output capabilities.

Unformatted input/output

Get characters from file stream

std::fgetc, 
std::getc

int fgetc( std::FILE* stream ); int getc( std::FILE* stream );

Reads the next character from the given input stream.

parameter

stream

-

Read character source

return value

The character obtained on success, and EOF on failure.

If an end-of-file condition causes failure, the end-of-filestream indicator on is additionally set (see std::feof()). If some other error caused the failure, set the error indicator on (see std::ferror()).stream

 Call example

#include <cstdio>
#include <cstdlib>

int main()
{
    FILE* file = std::fopen("test.txt", "r");
    if (!file)
    {
        std::perror("File opening failed");
        return EXIT_FAILURE;
    }

    int c; // 注意：是 int 而非 char ，要求处理 EOF
    while ((c = std::fgetc(file)) != EOF)   // 标准 C I/O 文件读取循环
    {
        std::putchar(c);
    }

    if (std::ferror(file))
    {
        std::puts("I/O error when reading");
    }
    else if (std::feof(file))
    {
        std::puts("End of file reached successfully");
    }

    std::fclose(file);
    return 0;
}

output

Get a string from a file stream

std::fgets

char* fgets( char* str, int count, std::FILE* stream );

Reads up to count - 1 characters from the given file stream and stores them in strthe character array pointed to by . Analysis is terminated if a newline character is present or found at the end of the file, in which case stra newline character will be included. If bytes are read and no errors occur, a null strcharacter is written immediately after the last character written to .

If countless than 1, the behavior is undefined. It also does not specify whether to write null characters, if count==1.

parameter

str	-	pointer to an element of the char array
count	-	The maximum number of characters to write (typically strthe length of )
stream	-	read file stream from data source

return value

On success str, a null pointer on failure.

If an end-of-file condition causes failure, the end-of-filestream indicator on is set (see std::feof()). This only fails if it results in an unread character, in which case a null pointer is returned and the contents of the pointed to array are not changed (i.e. the first byte is not overwritten with a null character).str

If other error conditions caused the failure, set the errorstream indicator on it (see std::ferror()). The contents of the array pointed to are undefined (may not even be null-terminated).str

Call example

#include <iostream>
#include <cstdio>
#include <cstdlib>

int main()
{
    std::FILE* tmpf = std::tmpfile();
    std::fputs("Alan Turing\n", tmpf);
    std::fputs("John von Neumann\n", tmpf);
    std::fputs("Alonzo Church\n", tmpf);

    std::rewind(tmpf);
    char buf[8];
    while (std::fgets(buf, sizeof buf, tmpf) != NULL)
    {
        std::cout << '"' << buf << '"' << '\n';
    }
    return 0;
}

output