Formatted text output to streams.

§1. Registration. The main function here is modelled on the "minimum printf" function used as an example in Kernighan and Ritchie, Chapter 7, but because it prints to streams, it combines the traditional functions printf, sprintf and fprintf in one. It also contains a number of doohickeys to provide for a wider and extensible range of string interpolations.

Traditionally, in the C library, everything in the formatting string is literal except for % escapes: thus %d means "integer goes here", and so on. We follow this but allow extra % escapes unknown to K&R, and we also allow a further family of $ escapes intended for the debugging log only; these are restricted to streams flagged as for debugging and generally produce guru meditation numbers rather than user-friendly information.

Each escape, say %z, must be "registered" before use, and will be given one of the following categories:

define VACANT_ECAT 0        unregistered
define POINTER_ECAT 1       data to be printed is a pointer to a structure
define INTSIZED_ECAT 2      data to be printed is or fits into an integer
define WORDING_ECAT 3       data to be printed is a wording structure from inform7
define DIRECT_ECAT 4        data must be printed directly by the code below

§2. We'll start with % escapes, which generalise the familiar printf escapes such as %d. Cumbersomely, we need three sorts of escape: those where the variable argument token is a pointer, those where it's essentially an integer, and those where it's a structure used only in the Inform 7 compiler called a wording. The standard C typechecker can't generalise across these, so we have to do everything three times. (And then we have to do all that twice, because the loggers don't use format strings.)

int escapes_registered = FALSE;
int escapes_category[2][128];  one of the *_ECAT values above
void *the_escapes[2][128];  the function to call to implement this

typedef void (*writer_function)(text_stream *, char *, void *);
typedef void (*writer_function_I)(text_stream *, char *, int);
typedef void (*log_function)(text_stream *, void *);
typedef void (*log_function_I)(text_stream *, int);
    typedef void (*writer_function_W)(text_stream *, char *, wording);
    typedef void (*log_function_W)(text_stream *, wording);


void Writers::log_escape_usage(void) {
    for (int cat = 0; cat < 2; cat++) {
        char *alphanum = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
        LOG("Vacant escapes: %s: ", (cat == 0)?"%":"$");
        for (int i=0; alphanum[i]; i++)
            if (escapes_category[cat][(int) alphanum[i]] == VACANT_ECAT)
                LOG("%c", alphanum[i]);

§4. That gives us a number of front doors:

void Writers::register_writer(int esc, void (*f)(text_stream *, char *, void *)) {
    Writers::register_writer_p(0, esc, (void *) f, POINTER_ECAT);
void Writers::register_logger(int esc, void (*f)(text_stream *, void *)) {
    Writers::register_writer_p(1, esc, (void *) f, POINTER_ECAT);
void Writers::register_writer_I(int esc, void (*f)(text_stream *, char *, int)) {
    Writers::register_writer_p(0, esc, (void *) f, INTSIZED_ECAT);
void Writers::register_logger_I(int esc, void (*f)(text_stream *, int)) {
    Writers::register_writer_p(1, esc, (void *) f, INTSIZED_ECAT);
#define Writers::register_writer_W(esc, f) Writers::register_writer_p(0, esc, (void *) f, WORDING_ECAT);
#define Writers::register_logger_W(esc, f) Writers::register_writer_p(1, esc, (void *) f, WORDING_ECAT);

§5. All leading to:

void Writers::register_writer_p(int set, int esc, void *f, int cat) {
    if (escapes_registered == FALSE) Initialise the table of escapes5.1;
    if ((esc < 0) || (esc >= 128) ||
        ((Characters::isalpha((wchar_t) esc) == FALSE) &&
            (Characters::isdigit((wchar_t) esc) == FALSE)))
        internal_error("nonalphabetic escape");
    if (escapes_category[set][esc] != VACANT_ECAT) {
        WRITE_TO(STDERR, "Clashing escape is %s%c\n", (set == 0)?"%":"$", esc);
        internal_error("clash of escapes");
    escapes_category[set][esc] = cat;
    the_escapes[set][esc] = f;

§5.1. We're going to implement %d and a few others directly, so those are marked in the table as being unavailable for registration.

Note that we don't support %f for floats; but we do add our very own %w for wide strings.

Initialise the table of escapes5.1 =

    escapes_registered = TRUE;
    for (int e=0; e<2; e++)
        for (int i=0; i<128; i++) {
            the_escapes[e][i] = NULL; escapes_category[e][i] = VACANT_ECAT;
    escapes_category[0]['c'] = DIRECT_ECAT;
    escapes_category[0]['d'] = DIRECT_ECAT;
    escapes_category[0]['g'] = DIRECT_ECAT;
    escapes_category[0]['i'] = DIRECT_ECAT;
    escapes_category[0]['s'] = DIRECT_ECAT;
    escapes_category[0]['w'] = DIRECT_ECAT;
    escapes_category[0]['x'] = DIRECT_ECAT;
    escapes_category[0]['%'] = DIRECT_ECAT;
    escapes_category[0]['$'] = DIRECT_ECAT;
    escapes_category[1]['%'] = DIRECT_ECAT;
    escapes_category[1]['$'] = DIRECT_ECAT;

§6. Writing. We can finally get on with that formatted-print function we've all been waiting for:

void Writers::printf(text_stream *stream, char *fmt, ...) {
    va_list ap;  the variable argument list signified by the dots
    char *p;
    if (stream == NULL) return;
    va_start(ap, fmt);  macro to begin variable argument processing
    for (p = fmt; *p; p++) {
        switch (*p) {
            case '%': {
                int set = 0; Deal with escape sequences6.1;
            case '$': {
                int set = 1;
                if ((stream->stream_flags) & USES_LOG_ESCAPES_STRF)
                    Deal with escape sequences6.1
                else Streams::putc('$', stream);
            case '"':
                if (stream->stream_flags & USES_I6_ESCAPES_STRF)
                    Streams::putc('~', stream);
                else Streams::putc(*p, stream);
            case '\n':
                Streams::putc(*p, stream);
            default: Streams::putc(*p, stream); break;
    va_end(ap);  macro to end variable argument processing

§6.1. Deal with escape sequences6.1 =

    char format_string[8];
    int esc_number = ' ';
    int i = 0;
    format_string[i++] = *(p++);
    while (*p) {
        format_string[i++] = *p;
        if ((islower(*p)) || (isupper(*p)) || ((set == 1) && (isdigit(*p))) ||
            (*p == '%')) esc_number = (int) *p;
        if ((esc_number != ' ') || (i==6)) break;
    format_string[i] = 0; p--;
    if ((esc_number<0) || (esc_number > 255)) esc_number = 0;
    switch (escapes_category[set][esc_number]) {
        case POINTER_ECAT: {
            if (set == 0) {
                writer_function f = (writer_function) the_escapes[0][esc_number];
                void *q = va_arg(ap, void *);
                (*f)(stream, format_string+1, q);
            } else {
                log_function f = (log_function) the_escapes[1][esc_number];
                void *q = va_arg(ap, void *);
                (*f)(stream, q);
        case INTSIZED_ECAT: {
            if (set == 0) {
                writer_function_I f = (writer_function_I) the_escapes[0][esc_number];
                int N = va_arg(ap, int);
                (*f)(stream, format_string+1, N);
            } else {
                log_function_I f = (log_function_I) the_escapes[1][esc_number];
                int N = va_arg(ap, int);
                (*f)(stream, N);
        case WORDING_ECAT: {
            #ifdef WORDS_MODULE
            if (set == 0) {
                writer_function_W f = (writer_function_W) the_escapes[0][esc_number];
                wording W = va_arg(ap, wording);
                (*f)(stream, format_string+1, W);
            } else {
                log_function_W f = (log_function_W) the_escapes[1][esc_number];
                wording W = va_arg(ap, wording);
                (*f)(stream, W);
        case DIRECT_ECAT: Implement this using the original printf6.1.1; break;
        case VACANT_ECAT:
            WRITE_TO(STDERR, "*** Bad WRITE escape: <%s> ***\n", format_string);
            internal_error("Unknown string escape");

§6.1.1. Here the traditional C library helps us out with the difficult ones to get right. We don't trouble to check that correct printf escapes have been used: instead, we pass anything in the form of a percentage sign, followed by up to four nonalphabetic modifying characters, followed by an alphabetic category character for numerical printing, straight through to sprintf or fprintf.

Thus an escape like %04d is handled by the standard C library, but not %s, which we handle directly. That's for two reasons: first, we want to be careful to prevent overruns of memory streams; second, we need to ensure that the correct encoding is used when writing to disc. The numerical escapes involve only characters whose representation is the same in all our file encodings, but expanding %s does not.

Implement this using the original printf6.1.1 =

    #pragma clang diagnostic push
    #pragma clang diagnostic ignored "-Wformat-nonliteral"
    switch (esc_number) {
        case 'c': {  char is promoted to int in variable arguments
            int ival = va_arg(ap, int);
            Streams::putc(ival, stream);
        case 'd': case 'i': case 'x': {
            int ival = va_arg(ap, int);
            char temp[256];
            if (snprintf(temp, 255, format_string, ival) >= 255) strcpy(temp, "?");
            for (int j = 0; temp[j]; j++) Streams::putc(temp[j], stream);
        case 'g': {
            double dval = va_arg(ap, double);
            char temp[256];
            if (snprintf(temp, 255, format_string, dval) >= 255) strcpy(temp, "?");
            for (int j = 0; temp[j]; j++) Streams::putc(temp[j], stream);
        case 's':
            for (char *sval = va_arg(ap, char *); *sval; sval++) Streams::putc(*sval, stream);
        case 'w': {
            wchar_t *W = (wchar_t *) va_arg(ap, wchar_t *);
            for (int j = 0; W[j]; j++) Streams::putc(W[j], stream);
        case '%': Streams::putc('%', stream); break;
        case '$': Streams::putc('$', stream); break;
    #pragma clang diagnostic pop

§7. Abbreviation macros. The following proved convenient for Inform, at any rate.

define REGISTER_WRITER(c, f) Writers::register_logger(c, &f##_writer);
define COMPILE_WRITER(t, f)
    void f##_writer(text_stream *format, void *obj) { text_stream *SDL = DL; DL = format; if (DL) f((t) obj); DL = SDL; }
define REGISTER_WRITER_I(c, f) Writers::register_logger_I(c, &f##_writer);
define COMPILE_WRITER_I(t, f)
    void f##_writer(text_stream *format, int I) { text_stream *SDL = DL; DL = format; if (DL) f((t) I); DL = SDL; }