自学教程：C++ vscnprintf函数代码示例

void_log_stderr(const char *fmt, ...){    struct logger *l = &logger;    int len, size, errno_save;    char buf[4 * LOG_MAX_LEN];    va_list args;    ssize_t n;    errno_save = errno;    len = 0;                /* length of output buffer */    size = 4 * LOG_MAX_LEN; /* size of output buffer */    va_start(args, fmt);    len += vscnprintf(buf, size, fmt, args);    va_end(args);    buf[len++] = '/n';    n = clive_write(STDERR_FILENO, buf, len);    if (n < 0) {        l->nerror++;    }    errno = errno_save;}

void __trace_note_message(struct blk_trace *bt, const char *fmt, ...){	int n;	va_list args;	unsigned long flags;	char *buf;	if (unlikely(bt->trace_state != Blktrace_running &&		     !blk_tracer_enabled))		return;	/*	 * If the BLK_TC_NOTIFY action mask isn't set, don't send any note	 * message to the trace.	 */	if (!(bt->act_mask & BLK_TC_NOTIFY))		return;	local_irq_save(flags);	buf = per_cpu_ptr(bt->msg_data, smp_processor_id());	va_start(args, fmt);	n = vscnprintf(buf, BLK_TN_MAX_MSG, fmt, args);	va_end(args);	trace_note(bt, 0, BLK_TN_MESSAGE, buf, n);	local_irq_restore(flags);}

static int dprintk(int level, const char *fmt, ...){	static char printk_buf[1024];	static long prevticks;	static int invocation;	va_list args;	int len;	if (level > USB_S3C2410_DEBUG_LEVEL)		return 0;	if (s3c2410_ticks != prevticks) {		prevticks = s3c2410_ticks;		invocation = 0;	}	len = scnprintf(printk_buf,			sizeof(printk_buf), "%1lu.%02d USB: ",			prevticks, invocation++);	va_start(args, fmt);	len = vscnprintf(printk_buf+len,			sizeof(printk_buf)-len, fmt, args);	va_end(args);	return pr_debug("%s", printk_buf);}

int printf(const char *fmt, ...){	va_list args;	uint i;	char printbuffer[CONFIG_SYS_PBSIZE];#ifndef CONFIG_PRE_CONSOLE_BUFFER	if (!gd->have_console)#ifdef CONFIG_SPL_SEMIHOSTING_SUPPORT		;	/* printf can be done with semihosting */#else		return 0;#endif	/* CONFIG_SPL_SEMIHOSTING_SUPPORT */#endif	/* CONFIG_PRE_CONSOLE_BUFFER */	va_start(args, fmt);	/* For this to work, printbuffer must be larger than	 * anything we ever want to print.	 */	i = vscnprintf(printbuffer, sizeof(printbuffer), fmt, args);	va_end(args);	/* Print the string */	puts(printbuffer);	return i;}

/*  * Function: report  * Description: Packet and Send data to userspace by kstate  * Input: mask -- message mask  *        fmt -- string  * Return: -1--failed, 0--success**/static int report(int mask, va_list args, const char *fmt){	int ret = -1;	struct kcollect_info info;	struct timeval time;	int length = 0;	size_t info_len = 0;	memset(&info, 0, sizeof(info));	length = vscnprintf(info.buffer, KCOLLECT_BUFFER_SIZE - 1, fmt, args);	if (length > 0) {		info.mask = mask;		info.len = length + 1;		if (!get_ktime_disable()) {			do_gettimeofday(&time);		}		info.tv_sec = (u32)time.tv_sec;		info.tv_usec = (u32)time.tv_usec;		info_len = sizeof(info) - KCOLLECT_BUFFER_SIZE + length + 1;		ret = kstate(CHANNEL_ID_KCOLLECT, PACKET_TAG_KCOLLECT, (char*)&info, info_len);		if (ret < 0) {			pr_err("hw_kcollect %s: kstate error/n", __func__);			ret = -1;		}	}	pr_debug("hw_kcollect %s: length=%d mask=%d/n", __func__, length, mask);	return ret;}

static void early_vprintk(const char *fmt, va_list ap){	if (early_console) {		char buf[512];		int n = vscnprintf(buf, sizeof(buf), fmt, ap);		early_console->write(early_console, buf, n);	}}

void _mali_osk_ctxprintf(_mali_osk_print_ctx *print_ctx, const char *fmt, ...){	va_list args;	char buf[512];	va_start(args, fmt);	vscnprintf(buf, 512, fmt, args);	seq_printf(print_ctx, buf);	va_end(args);}

/** * gpio_requestf() - [COMPAT] Request GPIO * @gpio:	GPIO number * @fmt:	Format string for the requested GPIO * @...:	Arguments for the printf() format string * * This function implements the API that's compatible with current * GPIO API used in U-Boot. The request is forwarded to particular * GPIO driver. Returns 0 on success, negative value on error. */int gpio_requestf(unsigned gpio, const char *fmt, ...){	va_list args;	char buf[40];	va_start(args, fmt);	vscnprintf(buf, sizeof(buf), fmt, args);	va_end(args);	return gpio_request(gpio, buf);}

static int dm_gpio_requestf(struct gpio_desc *desc, const char *fmt, ...){	va_list args;	char buf[40];	va_start(args, fmt);	vscnprintf(buf, sizeof(buf), fmt, args);	va_end(args);	return dm_gpio_request(desc, buf);}

u32 _mali_osk_snprintf(char *buf, u32 size, const char *fmt, ...){	int res;	va_list args;	va_start(args, fmt);	res = vscnprintf(buf, (size_t)size, fmt, args);	va_end(args);	return res;}

static u32 write_str(struct debug_buffer *buffer, const char *fmt, ...){	va_list args;	u32 size;	va_start(args, fmt);	size = vscnprintf(buffer->curr, MAX_DBG_BUF_SIZE - 1, fmt, args);	va_end(args);	buffer->curr += size;	buffer->filled_size += size;	return size;}

void notrace prom_printf(const char *fmt, ...){	va_list args;	int i;	va_start(args, fmt);	i = vscnprintf(ppbuf, sizeof(ppbuf), fmt, args);	va_end(args);	prom_write(ppbuf, i);}

/**    @function: int srecorder_snprintf(char *buf, size_t size, const char *fmt, ...)    @brief: 按指定格式输出字符串到指定缓存中。    @param: buf 缓存    @param: size 缓存空间大小    @param: fmt 字符串格式    @return: 写入缓存的字节数    @note:*/int srecorder_snprintf(char *buf, size_t size, const char *fmt, ...){    va_list args;    int i = 0;    va_start(args, fmt);    i = vscnprintf(buf, size, fmt, args);    va_end(args);    return i;}

static intscnprintf(char *buf, size_t size, const char *fmt, ...){    va_list args;    int n;    va_start(args, fmt);    n = vscnprintf(buf, size, fmt, args);    va_end(args);    return n;}

void hsu_early_printk(const char *fmt, ...){	char buf[512];	int n;	va_list ap;	va_start(ap, fmt);	n = vscnprintf(buf, 512, fmt, ap);	va_end(ap);	early_hsu_console.write(&early_hsu_console, buf, n);}

int vprintf(const char *fmt, va_list args){	char printk_buf[MAX_PRINTF_SIZE];	int printed_len;	printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);	printk_buf[printed_len] = '/0';										/* vscnprintf函数返回的值永远不会大于printk_buf数组的长度 */	console_write(printk_buf, printed_len);	return printed_len;}

int cfe_vprintk(const char *fmt, va_list args){	static char buffer[1024];	static DEFINE_SPINLOCK(lock);	static const char pfx[] = "CFE-console: ";	static const size_t pfx_len = sizeof(pfx) - 1;	unsigned long flags;	int len, cnt, pos;	int handle;	int res;	if (!cfe_present())		return -ENODEV;	spin_lock_irqsave(&lock, flags);	handle = cfe_getstdhandle(CFE_STDHANDLE_CONSOLE);	if (CFE_ISERR(handle)) {		len = -EIO;		goto out;	}	strcpy(buffer, pfx);	len = vscnprintf(buffer + pfx_len,			 sizeof(buffer) - pfx_len - 2,			 fmt, args);	len += pfx_len;	/* The CFE console requires CR-LF line-ends.	 * Add a CR, if we only terminate lines with a LF.	 * This does only fix CR-LF at the end of the string.	 * So for multiple lines, use multiple cfe_vprintk calls.	 */	if (len > 1 &&	    buffer[len - 1] == '/n' && buffer[len - 2] != '/r') {		buffer[len - 1] = '/r';		buffer[len] = '/n';		len += 1;	}	cnt = len;	pos = 0;	while (cnt > 0) {		res = cfe_write(handle, buffer + pos, len - pos);		if (CFE_ISERR(res)) {			len = -EIO;			goto out;		}		cnt -= res;		pos += res;	}out:	spin_unlock_irqrestore(&lock, flags);	return len;}

static int wl1271_format_buffer(char __user *userbuf, size_t count,				    loff_t *ppos, char *fmt, ...){	va_list args;	char buf[DEBUGFS_FORMAT_BUFFER_SIZE];	int res;	va_start(args, fmt);	res = vscnprintf(buf, sizeof(buf), fmt, args);	va_end(args);	return simple_read_from_buffer(userbuf, count, ppos, buf, res);}

int debug_log(struct bat_priv *bat_priv, const char *fmt, ...){	va_list args;	char tmp_log_buf[256];	va_start(args, fmt);	vscnprintf(tmp_log_buf, sizeof(tmp_log_buf), fmt, args);	fdebug_log(bat_priv->debug_log, "[%10lu] %s",		   (jiffies / HZ), tmp_log_buf);	va_end(args);	return 0;}

void pdc_printf(const char *fmt, ...){	va_list args;	char buf[1024];	int i, len;	va_start(args, fmt);	len = vscnprintf(buf, sizeof(buf), fmt, args);	va_end(args);	for (i = 0; i < len; i++)		pdc_iodc_outc(buf[i]);}

/** * batadv_debug_log() - Add debug log entry * @bat_priv: the bat priv with all the soft interface information * @fmt: format string * * Return: 0 on success or negative error number in case of failure */int batadv_debug_log(struct batadv_priv *bat_priv, const char *fmt, ...){	va_list args;	char tmp_log_buf[256];	va_start(args, fmt);	vscnprintf(tmp_log_buf, sizeof(tmp_log_buf), fmt, args);	batadv_fdebug_log(bat_priv->debug_log, "[%10u] %s",			  jiffies_to_msecs(jiffies), tmp_log_buf);	va_end(args);	return 0;}

static void fiq_watchdog_printf(struct fiq_debugger_output *output,				const char *fmt, ...){	char buf[256];	va_list ap;	int len;	va_start(ap, fmt);	len = vscnprintf(buf, sizeof(buf), fmt, ap);	va_end(ap);	ramoops_console_write_buf(buf, len);}

void early_printk(const char *fmt, ...){	char buf[512];	int n;	va_list ap;	if (early_console_initialized) {		va_start(ap, fmt);		n = vscnprintf(buf, 512, fmt, ap);		early_console->write(early_console, buf, n);		va_end(ap);	}}

int printf(const char *fmt, ...){	va_list args;	int len;	char outbuf[256];	va_start(args, fmt);	len = vscnprintf(outbuf, sizeof(outbuf), fmt, args);	va_end(args);	outbuf[len] = 0;	putsnonl(outbuf);	return len;}

int telnet_printf(const char *fmt, ...){	va_list args;	int len;	char outbuf[TELNET_PRINTF_BUFFER_SIZE];	va_start(args, fmt);	len = vscnprintf(outbuf, sizeof(outbuf), fmt, args);	va_end(args);	outbuf[len] = 0;	telnet_putsnonl(outbuf);	return len;}

/** * gpio_requestf() - [COMPAT] Request GPIO * @gpio:	GPIO number * @fmt:	Format string for the requested GPIO * @...:	Arguments for the printf() format string * * This function implements the API that's compatible with current * GPIO API used in U-Boot. The request is forwarded to particular * GPIO driver. Returns 0 on success, negative value on error. */int gpio_requestf(unsigned gpio, const char *fmt, ...){#if !defined(CONFIG_SPL_BUILD) || !defined(CONFIG_USE_TINY_PRINTF)	va_list args;	char buf[40];	va_start(args, fmt);	vscnprintf(buf, sizeof(buf), fmt, args);	va_end(args);	return gpio_request(gpio, buf);#else	return gpio_request(gpio, fmt);#endif}

static int dm_gpio_requestf(struct gpio_desc *desc, const char *fmt, ...){#if !defined(CONFIG_SPL_BUILD) || !defined(CONFIG_USE_TINY_PRINTF)	va_list args;	char buf[40];	va_start(args, fmt);	vscnprintf(buf, sizeof(buf), fmt, args);	va_end(args);	return dm_gpio_request(desc, buf);#else	return dm_gpio_request(desc, fmt);#endif}