std::fgets

 

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File access fopen freopen fclose fflush fwide setbuf setvbuf Direct input/output fread fwrite Unformatted input/output fgetcgetc fgets fputcputc fputs getchar gets (until C++14) putchar puts ungetc fgetwcgetwc fgetws fputwcputwc fputws getwchar putwchar ungetwc Formatted input scanffscanfsscanf vscanfvfscanfvsscanf (C++11)(C++11)(C++11)     wscanffwscanfswscanf vwscanfvfwscanfvswscanf (C++11)(C++11)(C++11)	Formatted output printffprintfsprintfsnprintf (C++11) vprintfvfprintfvsprintfvsnprintf (C++11)     wprintffwprintfswprintf vwprintfvfwprintfvswprintf File positioning ftell fgetpos fseek fsetpos rewind Error handling clearerr feof ferror perror Operations on files remove rename tmpfile tmpnam

 

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 <cstdio>#include <cstdlib>#include <iomanip>#include <iostream>#include <span>   void dump(std::span<constchar> 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);   std::rewind(tmpf);for(char buf[8]; std::fgets(buf, sizeof buf, tmpf)!= nullptr;) dump(buf, 10);}

Output:

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

See also

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