NAME

std::fgets - std::fgets

Synopsis

Defined in header <cstdio>
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

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

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

// Run this code

#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';
}
}

Output:

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