Macros¶

Typedefs¶

Functions¶

Introduction to the Standard IO facilities¶

Due to space constraints, some functionality has not been implemented at all (like some of the printf conversions that have been left out). Nevertheless, potential users of this implementation should be warned: the printf and scanf families of functions, although usually associated with presumably simple things like the famous 'Hello, world!' program, are actually fairly complex which causes their inclusion to eat up a fair amount of code space. Also, they are not fast due to the nature of interpreting the format string at run-time. Whenever possible, resorting to the (sometimes non-standard) predetermined conversion facilities that are offered by avr-libc will usually cost much less in terms of speed and code size.

Tunable options for code size vs. feature set¶

Outline of the chosen API¶

As an alternative method to fdevopen(), the macro fdev_setup_stream() might be used to setup a user-supplied FILE structure.

It should be noted that the automatic conversion of a newline character into a carriage return - newline sequence breaks binary transfers. If binary transfers are desired, no automatic conversion should be performed, but instead any string that aims to issue a CR-LF sequence must use '\r\n' explicitly.

For convenience, the first call to fdevopen() that opens a stream for reading will cause the resulting stream to be aliased to stdin. Likewise, the first call to fdevopen() that opens a stream for writing will cause the resulting stream to be aliased to both, stdout, and stderr. Thus, if the open was done with both, read and write intent, all three standard streams will be identical. Note that these aliases are indistinguishable from each other, thus calling fclose() on such a stream will also effectively close all of its aliases (note 3).

It is possible to tie additional user data to a stream, using fdev_set_udata(). The backend put and get functions can then extract this user data using fdev_get_udata(), and act appropriately. For example, a single put function could be used to talk to two different UARTs that way, or the put and get functions could keep internal state between calls there.

Format strings in flash ROM¶

Running stdio without malloc()¶

The macro fdev_setup_stream() is provided to prepare a user-supplied FILE buffer for operation with stdio.

Example¶

#include <stdio.h>
static int uart_putchar(char c, FILE *stream);
static FILE mystdout = FDEV_SETUP_STREAM(uart_putchar, NULL,
                                         _FDEV_SETUP_WRITE);
static int
uart_putchar(char c, FILE *stream)
{
  if (c == '0)
    uart_putchar('', stream);
  loop_until_bit_is_set(UCSRA, UDRE);
  UDR = c;
  return 0;
}
int
main(void)
{
  init_uart();
  stdout = &mystdout;
  printf("Hello, world!0);
  return 0;
}

This example uses the initializer form FDEV_SETUP_STREAM() rather than the function-like fdev_setup_stream(), so all data initialization happens during C start-up.

If streams initialized that way are no longer needed, they can be destroyed by first calling the macro fdev_close(), and then destroying the object itself. No call to fclose() should be issued for these streams. While calling fclose() itself is harmless, it will cause an undefined reference to free() and thus cause the linker to link the malloc module into the application.

Notes¶

Note 2:

int
uart_putchar(char c, FILE *stream)
{
  if (c == '0)
    uart_putchar('');
  loop_until_bit_is_set(UCSRA, UDRE);
  UDR = c;
  return 0;
}

Note 3:

#define _FDEV_EOF (-2)¶

To be used in the get function of fdevopen().

#define _FDEV_ERR (-1)¶

To be used in the get function of fdevopen().

#define _FDEV_SETUP_READ __SRD¶

#define _FDEV_SETUP_RW (__SRD|__SWR)¶

#define _FDEV_SETUP_WRITE __SWR¶

#define EOF (-1)¶

#define fdev_close()¶

(Currently, this macro evaluates to nothing, but this might change in future versions of the library.)

#define fdev_get_udata(stream) ((stream)->udata)¶

#define fdev_set_udata(stream, u) do { (stream)->udata = u; } while(0)¶

The user data can be useful for tracking state in the put and get functions supplied to the fdevopen() function.

#define fdev_setup_stream(stream, put, get, rwflag)¶

The arguments put and get are identical to those that need to be passed to fdevopen().

The rwflag argument can take one of the values _FDEV_SETUP_READ, _FDEV_SETUP_WRITE, or _FDEV_SETUP_RW, for read, write, or read/write intent, respectively.

Note:

#define FDEV_SETUP_STREAM(put, get, rwflag)¶

The remaining arguments are to be used as explained in fdev_setup_stream().

#define getc(__stream) fgetc(__stream)¶

#define getchar(void) fgetc(stdin)¶

#define putc(__c, __stream) fputc(__c, __stream)¶

#define putchar(__c) fputc(__c, stdout)¶

#define stderr (__iob[2])¶

If stderr should point to another stream, the result of another fdevopen() must be explicitly assigned to it without closing the previous stderr (since this would also close stdout).

#define stdin (__iob[0])¶

The first stream opened with read intent using fdevopen() will be assigned to stdin.

#define stdout (__iob[1])¶

The first stream opened with write intent using fdevopen() will be assigned to both, stdin, and stderr.

typedef struct __file FILE¶

void clearerr (FILE * __stream)¶

int fclose (FILE * __stream)¶

When using fdevopen() to setup the stream, a call to fclose() is needed in order to free the internal resources allocated.

If the stream has been set up using fdev_setup_stream() or FDEV_SETUP_STREAM(), use fdev_close() instead.

It currently always returns 0 (for success).

FILE* fdevopen (int(*)(char, FILE *) put, int(*)(FILE *) get)¶

It opens a stream for a device where the actual device implementation needs to be provided by the application. If successful, a pointer to the structure for the opened stream is returned. Reasons for a possible failure currently include that neither the put nor the get argument have been provided, thus attempting to open a stream with no IO intent at all, or that insufficient dynamic memory is available to establish a new stream.

If the put function pointer is provided, the stream is opened with write intent. The function passed as put shall take two arguments, the first a character to write to the device, and the second a pointer to FILE, and shall return 0 if the output was successful, and a nonzero value if the character could not be sent to the device.

If the get function pointer is provided, the stream is opened with read intent. The function passed as get shall take a pointer to FILE as its single argument, and return one character from the device, passed as an int type. If an error occurs when trying to read from the device, it shall return _FDEV_ERR. If an end-of-file condition was reached while reading from the device, _FDEV_EOF shall be returned.

If both functions are provided, the stream is opened with read and write intent.

The first stream opened with read intent is assigned to stdin, and the first one opened with write intent is assigned to both, stdout and stderr.

fdevopen() uses calloc() (und thus malloc()) in order to allocate the storage for the new stream.

Note:

int feof (FILE * __stream)¶

int ferror (FILE * __stream)¶

int fflush (FILE * stream)¶

This is a null operation provided for source-code compatibility only, as the standard IO implementation currently does not perform any buffering.

int fgetc (FILE * __stream)¶

char* fgets (char * __str, int __size, FILE * __stream)¶

If an error was encountered, the function returns NULL and sets the error flag of stream, which can be tested using ferror(). Otherwise, a pointer to the string will be returned.

int fprintf (FILE * __stream, const char * __fmt, ...)¶

int fprintf_P (FILE * __stream, const char * __fmt, ...)¶

int fputc (int __c, FILE * __stream)¶

int fputs (const char * __str, FILE * __stream)¶

Returns 0 on success and EOF on error.

int fputs_P (const char * __str, FILE * __stream)¶

size_t fread (void * __ptr, size_t __size, size_t __nmemb, FILE * __stream)¶

Returns the number of objects successfully read, i. e. nmemb unless an input error occured or end-of-file was encountered. feof() and ferror() must be used to distinguish between these two conditions.

int fscanf (FILE * __stream, const char * __fmt, ...)¶

See vfscanf() for details.

int fscanf_P (FILE * __stream, const char * __fmt, ...)¶

size_t fwrite (const void * __ptr, size_t __size, size_t __nmemb, FILE * __stream)¶

Returns the number of objects successfully written, i. e. nmemb unless an output error occured.

char* gets (char * __str)¶

int printf (const char * __fmt, ...)¶

int printf_P (const char * __fmt, ...)¶

int puts (const char * __str)¶

int puts_P (const char * __str)¶

int scanf (const char * __fmt, ...)¶

See vfscanf() for details.

int scanf_P (const char * __fmt, ...)¶

int snprintf (char * __s, size_t __n, const char * __fmt, ...)¶

Returns the number of characters that would have been written to s if there were enough space.

int snprintf_P (char * __s, size_t __n, const char * __fmt, ...)¶

int sprintf (char * __s, const char * __fmt, ...)¶

int sprintf_P (char * __s, const char * __fmt, ...)¶

int sscanf (const char * __buf, const char * __fmt, ...)¶

See vfscanf() for details.

int sscanf_P (const char * __buf, const char * __fmt, ...)¶

int ungetc (int __c, FILE * __stream)¶

Currently, only a single character can be pushed back onto the stream.

The ungetc() function returns the character pushed back after the conversion, or EOF if the operation fails. If the value of the argument c character equals EOF, the operation will fail and the stream will remain unchanged.

int vfprintf (FILE * __stream, const char * __fmt, va_list __ap)¶

vfprintf returns the number of characters written to stream, or EOF in case of an error. Currently, this will only happen if stream has not been opened with write intent.

The format string is composed of zero or more directives: ordinary characters (not %), which are copied unchanged to the output stream; and conversion specifications, each of which results in fetching zero or more subsequent arguments. Each conversion specification is introduced by the % character. The arguments must properly correspond (after type promotion) with the conversion specifier. After the %, the following appear in sequence:

•

Zero or more of the following flags:

•

# The value should be converted to an 'alternate form'. For c, d, i, s, and u conversions, this option has no effect. For o conversions, the precision of the number is increased to force the first character of the output string to a zero (except if a zero value is printed with an explicit precision of zero). For x and X conversions, a non-zero result has the string `0x' (or `0X' for X conversions) prepended to it.

•

0 (zero) Zero padding. For all conversions, the converted value is padded on the left with zeros rather than blanks. If a precision is given with a numeric conversion (d, i, o, u, i, x, and X), the 0 flag is ignored.

•

- A negative field width flag; the converted value is to be left adjusted on the field boundary. The converted value is padded on the right with blanks, rather than on the left with blanks or zeros. A - overrides a 0 if both are given.

•

•

+ A sign must always be placed before a number produced by a signed conversion. A + overrides a space if both are used.

• An optional decimal digit string specifying a minimum field width. If the converted value has fewer characters than the field width, it will be padded with spaces on the left (or right, if the left-adjustment flag has been given) to fill out the field width.
• An optional precision, in the form of a period . followed by an optional digit string. If the digit string is omitted, the precision is taken as zero. This gives the minimum number of digits to appear for d, i, o, u, x, and X conversions, or the maximum number of characters to be printed from a string for s conversions.
• An optional l or h length modifier, that specifies that the argument for the d, i, o, u, x, or X conversion is a 'long int' rather than int. The h is ignored, as 'short int' is equivalent to int.
• A character that specifies the type of conversion to be applied.

The conversion specifiers and their meanings are:

• diouxX The int (or appropriate variant) argument is converted to signed decimal (d and i), unsigned octal (o), unsigned decimal (u), or unsigned hexadecimal (x and X) notation. The letters 'abcdef' are used for x conversions; the letters 'ABCDEF' are used for X conversions. The precision, if any, gives the minimum number of digits that must appear; if the converted value requires fewer digits, it is padded on the left with zeros.
• p The void * argument is taken as an unsigned integer, and converted similarly as a %#x command would do.
• c The int argument is converted to an 'unsigned char', and the resulting character is written.
• s The 'char *' argument is expected to be a pointer to an array of character type (pointer to a string). Characters from the array are written up to (but not including) a terminating NUL character; if a precision is specified, no more than the number specified are written. If a precision is given, no null character need be present; if the precision is not specified, or is greater than the size of the array, the array must contain a terminating NUL character.
• % A % is written. No argument is converted. The complete conversion specification is '%%'.
• eE The double argument is rounded and converted in the format '[-]d.ddde±dd' where there is one digit before the decimal-point character and the number of digits after it is equal to the precision; if the precision is missing, it is taken as 6; if the precision is zero, no decimal-point character appears. An E conversion uses the letter 'E' (rather than 'e') to introduce the exponent. The exponent always contains two digits; if the value is zero, the exponent is 00.
• fF The double argument is rounded and converted to decimal notation in the format '[-]ddd.ddd', where the number of digits after the decimal-point character is equal to the precision specification. If the precision is missing, it is taken as 6; if the precision is explicitly zero, no decimal-point character appears. If a decimal point appears, at least one digit appears before it.
• gG The double argument is converted in style f or e (or F or E for G conversions). The precision specifies the number of significant digits. If the precision is missing, 6 digits are given; if the precision is zero, it is treated as 1. Style e is used if the exponent from its conversion is less than -4 or greater than or equal to the precision. Trailing zeros are removed from the fractional part of the result; a decimal point appears only if it is followed by at least one digit.
• S Similar to the s format, except the pointer is expected to point to a program-memory (ROM) string instead of a RAM string.

In no case does a non-existent or small field width cause truncation of a numeric field; if the result of a conversion is wider than the field width, the field is expanded to contain the conversion result.

Since the full implementation of all the mentioned features becomes fairly large, three different flavours of vfprintf() can be selected using linker options. The default vfprintf() implements all the mentioned functionality except floating point conversions. A minimized version of vfprintf() is available that only implements the very basic integer and string conversion facilities, but only the # additional option can be specified using conversion flags (these flags are parsed correctly from the format specification, but then simply ignored). This version can be requested using the following compiler options:

-Wl,-u,vfprintf -lprintf_min

If the full functionality including the floating point conversions is required, the following options should be used:

-Wl,-u,vfprintf -lprintf_flt -lm

Limitations:

Notes:

int vfprintf_P (FILE * __stream, const char * __fmt, va_list __ap)¶

int vfscanf (FILE * stream, const char * fmt, va_list ap)¶

Characters are read from stream and processed in a way described by fmt. Conversion results will be assigned to the parameters passed via ap.

The format string fmt is scanned for conversion specifications. Anything that doesn't comprise a conversion specification is taken as text that is matched literally against the input. White space in the format string will match any white space in the data (including none), all other characters match only itself. Processing is aborted as soon as the data and format string no longer match, or there is an error or end-of-file condition on stream.

Most conversions skip leading white space before starting the actual conversion.

Conversions are introduced with the character %. Possible options can follow the %:

• a * indicating that the conversion should be performed but the conversion result is to be discarded; no parameters will be processed from ap,
• the character h indicating that the argument is a pointer to short int (rather than int),
• the 2 characters hh indicating that the argument is a pointer to char (rather than int).
• the character l indicating that the argument is a pointer to long int (rather than int, for integer type conversions), or a pointer to double (for floating point conversions),

In addition, a maximal field width may be specified as a nonzero positive decimal integer, which will restrict the conversion to at most this many characters from the input stream. This field width is limited to at most 255 characters which is also the default value (except for the c conversion that defaults to 1).

The following conversion flags are supported:

• % Matches a literal % character. This is not a conversion.
• d Matches an optionally signed decimal integer; the next pointer must be a pointer to int.
• i Matches an optionally signed integer; the next pointer must be a pointer to int. The integer is read in base 16 if it begins with 0x or 0X, in base 8 if it begins with 0, and in base 10 otherwise. Only characters that correspond to the base are used.
• o Matches an octal integer; the next pointer must be a pointer to unsigned int.
• u Matches an optionally signed decimal integer; the next pointer must be a pointer to unsigned int.
• x Matches an optionally signed hexadecimal integer; the next pointer must be a pointer to unsigned int.
• f Matches an optionally signed floating-point number; the next pointer must be a pointer to float.
• e, g, F, E, G Equivalent to f.
• s Matches a sequence of non-white-space characters; the next pointer must be a pointer to char, and the array must be large enough to accept all the sequence and the terminating NUL character. The input string stops at white space or at the maximum field width, whichever occurs first.
• c Matches a sequence of width count characters (default 1); the next pointer must be a pointer to char, and there must be enough room for all the characters (no terminating NUL is added). The usual skip of leading white space is suppressed. To skip white space first, use an explicit space in the format.
• [ Matches a nonempty sequence of characters from the specified set of accepted characters; the next pointer must be a pointer to char, and there must be enough room for all the characters in the string, plus a terminating NUL character. The usual skip of leading white space is suppressed. The string is to be made up of characters in (or not in) a particular set; the set is defined by the characters between the open bracket [ character and a close bracket ] character. The set excludes those characters if the first character after the open bracket is a circumflex ^. To include a close bracket in the set, make it the first character after the open bracket or the circumflex; any other position will end the set. The hyphen character - is also special; when placed between two other characters, it adds all intervening characters to the set. To include a hyphen, make it the last character before the final close bracket. For instance, [^]0-9-] means the set of everything except close bracket, zero through nine, and hyphen. The string ends with the appearance of a character not in the (or, with a circumflex, in) set or when the field width runs out. Note that usage of this conversion enlarges the stack expense.
• p Matches a pointer value (as printed by p in printf()); the next pointer must be a pointer to void.
• n Nothing is expected; instead, the number of characters consumed thus far from the input is stored through the next pointer, which must be a pointer to int. This is not a conversion, although it can be suppressed with the * flag.

These functions return the number of input items assigned, which can be fewer than provided for, or even zero, in the event of a matching failure. Zero indicates that, while there was input available, no conversions were assigned; typically this is due to an invalid input character, such as an alphabetic character for a d conversion. The value EOF is returned if an input failure occurs before any conversion such as an end-of-file occurs. If an error or end-of-file occurs after conversion has begun, the number of conversions which were successfully completed is returned.

By default, all the conversions described above are available except the floating-point conversions and the width is limited to 255 characters. The float-point conversion will be available in the extended version provided by the library libscanf_flt.a. Also in this case the width is not limited (exactly, it is limited to 65535 characters). To link a program against the extended version, use the following compiler flags in the link stage:

-Wl,-u,vfscanf -lscanf_flt -lm

A third version is available for environments that are tight on space. In addition to the restrictions of the standard one, this version implements no %[ specification. This version is provided in the library libscanf_min.a, and can be requested using the following options in the link stage:

-Wl,-u,vfscanf -lscanf_min -lm

int vfscanf_P (FILE * __stream, const char * __fmt, va_list __ap)¶

int vprintf (const char * __fmt, va_list __ap)¶

See vfprintf() for details.

int vscanf (const char * __fmt, va_list __ap)¶

See vfscanf() for details.

int vsnprintf (char * __s, size_t __n, const char * __fmt, va_list ap)¶

Returns the number of characters that would have been written to s if there were enough space.

int vsnprintf_P (char * __s, size_t __n, const char * __fmt, va_list ap)¶

int vsprintf (char * __s, const char * __fmt, va_list ap)¶

int vsprintf_P (char * __s, const char * __fmt, va_list ap)¶