单片机 mcu stm32 printf自定义

#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int write_format(int hd, const char *format, ...) {
    char *msg;
    va_list arg;
    int ret;

    /* compute the length of the formatted message */
    va_start(arg, format);
    ret = vsnprintf(NULL, 0, format, arg);
    va_end(arg);

    /* allocated an array for the formatted message */
    if (ret < 0 || (msg = malloc(ret + 1)) == NULL)
        return -1;

    /* construct the formatted message */
    va_start(arg, ap);
    ret = vsnprintf(msg, ret + 1, format, arg);
    va_end(arg);

    /* send the message using the write system call */
    ret = write(hd, msg, ret);

    free(msg);
    return ret;
}