< cpp‎ | io‎ | c
C-style I/O
Types and objects
File access
Direct input/output
Unformatted input/output
Formatted input
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.


[edit] 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

[edit] 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).

[edit] 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.

[edit] Example

#include <cstdio>
#include <cstdlib>
#include <iomanip>
#include <iostream>
#include <span>
void dump(std::span<const char> buf, std::size_t offset)
    std::cout << std::dec;
    for (char ch : buf)
        std::cout << (ch >= ' ' ? ch : '.'), offset--;
    std::cout << std::string(offset, ' ') << std::hex
              << std::setfill('0') << std::uppercase;
    for (unsigned ch : buf)
        std::cout << std::setw(2) << ch << ' ';
    std::cout << std::dec << '\n';
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);
    for (char buf[8]; std::fgets(buf, sizeof buf, tmpf) != nullptr;)
        dump(buf, 10);


Alan Tu.  41 6C 61 6E 20 54 75 00 
ring..u.  72 69 6E 67 0A 00 75 00 
John vo.  4A 6F 68 6E 20 76 6F 00 
n Neuma.  6E 20 4E 65 75 6D 61 00 
nn..uma.  6E 6E 0A 00 75 6D 61 00 
Alonzo .  41 6C 6F 6E 7A 6F 20 00 
Church..  43 68 75 72 63 68 0A 00

[edit] See also

reads formatted input from stdin, a file stream or a buffer
(function) [edit]
(deprecated in C++11)(removed in C++14)
reads a character string from stdin
(function) [edit]
writes a character string to a file stream
(function) [edit]
C documentation for fgets