使用标准库，编写stm32f103c8t6通过USART2串口打印的程序，上一个不能用

以下是使用标准库，在stm32f103c8t6上通过USART2串口打印的程序。

#include "stm32f10x.h"
#include <stdio.h>

void USART2_Init(void);
void USART2_SendChar(char ch);
void USART2_SendString(char* str);

int main(void)
{
    USART2_Init();
    
    while (1)
    {
        USART2_SendString("Hello, world!\r\n");
    }
}

void USART2_Init(void)
{
    GPIO_InitTypeDef GPIO_InitStructure;
    USART_InitTypeDef USART_InitStructure;

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA | RCC_APB2Periph_AFIO | RCC_APB2Periph_USART1, ENABLE);

    // Configure USART2 Tx (PA.2) as alternate function push-pull
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_2;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_Init(GPIOA, &GPIO_InitStructure);

    // Configure USART2 Rx (PA.3) as input floating
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_3;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
    GPIO_Init(GPIOA, &GPIO_InitStructure);

    // USART2 configuration
    USART_InitStructure.USART_BaudRate = 115200;
    USART_InitStructure.USART_WordLength = USART_WordLength_8b;
    USART_InitStructure.USART_StopBits = USART_StopBits_1;
    USART_InitStructure.USART_Parity = USART_Parity_No;
    USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;
    USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx;
    USART_Init(USART2, &USART_InitStructure);

    // Enable USART2
    USART_Cmd(USART2, ENABLE);
}

void USART2_SendChar(char ch)
{
    while (USART_GetFlagStatus(USART2, USART_FLAG_TXE) == RESET);
    USART_SendData(USART2, ch);
}

void USART2_SendString(char* str)
{
    while (*str)
    {
        USART2_SendChar(*str++);
    }
}

这个程序使用了USART2串口和PA2和PA3引脚。在main函数中，我们初始化了USART2，并在while循环中不断发送"Hello, world!\r\n"字符串。USART2_Init函数用于配置USART2，USART2_SendChar和USART2_SendString函数用于发送单个字符和字符串。