std::fgets

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

Reads at most count - 1 characters from the given file stream and stores them in the character array pointed to by str. Parsing stops if a newline character is found, in which case str will contain that newline character, or if end-of-file occurs. If bytes are read and no errors occur, writes a null character at the position immediately after the last character written to str.

Parameters

Return value

str on success, null pointer on failure.

If the end-of-file condition is encountered, sets the eof indicator on stream (see std::feof()). This is only a failure if it causes no bytes to be read, in which case a null pointer is returned and the contents of the array pointed to by str are not altered (i.e. the first byte is not overwritten with a null character).

If the failure has been caused by some other error, sets the error indicator (see std::ferror()) on stream. The contents of the array pointed to by str are indeterminate (it may not even be null-terminated).

Notes

POSIX additionally requires that fgets sets errno if it encounters a failure other than the end-of-file condition.

Although the standard specification is unclear in the cases where count<=1, common implementations do.

• if count < 1, do nothing, report error
• if count == 1,
• some implementations do nothing, report error,
• others read nothing, store zero in str[0], report success

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) != nullptr) {
        std::cout << '"' << buf << '"' << '\n';
    }
}

"Alan Tu"
"ring
"
"John vo"
"n Neuma"
"nn
"
"Alonzo "
"Church
"

See also