STM32新手指南：Hal库printf输出流重定向攻略

使用场景：

STM32单片机 HAL库printf函数重定向问题，无法在串口助手中收到数据的bug记录
编程IDE为：STM32CubeIDE
单片机型号为：STM32F103C8T6

问题描述

在使用stm32 HAL库的USART进行串口发送的过程中，发现重定向后的printf函数无法在串口中收到数据，而且编译没有报错

/* USER CODE BEGIN Header *//**
  ******************************************************************************
  * @file           : main.c
  * @brief          : Main program body
  ******************************************************************************
  * @attention
  *
  * Copyright (c) 2022 STMicroelectronics.
  * All rights reserved.
  *
  * This software is licensed under terms that can be found in the LICENSE file
  * in the root directory of this software component.
  * If no LICENSE file comes with this software, it is provided AS-IS.
  *
  ******************************************************************************
  *//* USER CODE END Header *//* Includes ------------------------------------------------------------------*/#include"main.h"#include"stdio.h"/* Private includes ----------------------------------------------------------*//* USER CODE BEGIN Includes *//* USER CODE END Includes *//* Private typedef -----------------------------------------------------------*//* USER CODE BEGIN PTD *//* USER CODE END PTD *//* Private define ------------------------------------------------------------*//* USER CODE BEGIN PD *//* USER CODE END PD *//* Private macro -------------------------------------------------------------*//* USER CODE BEGIN PM *//* USER CODE END PM *//* Private variables ---------------------------------------------------------*/
 I2C_HandleTypeDef hi2c1;
UART_HandleTypeDef huart1;/* USER CODE BEGIN PV *//* USER CODE END PV *//* Private function prototypes -----------------------------------------------*/voidSystemClock_Config(void);staticvoidMX_GPIO_Init(void);staticvoidMX_I2C1_Init(void);staticvoidMX_USART1_UART_Init(void);/* USER CODE BEGIN PFP *//* USER CODE END PFP *//* Private user code ---------------------------------------------------------*//* USER CODE BEGIN 0 */#ifdef__GNUC__#definePUTCHAR_PROTOTYPEint__io_putchar(int ch)#else#definePUTCHAR_PROTOTYPEintfputc(int ch, FILE *f)#endif
PUTCHAR_PROTOTYPE
{HAL_UART_Transmit(&huart1,(uint8_t*)&ch,1,0xFFFF);//阻塞方式打印return ch;}/* USER CODE END 0 *//**
  * @brief  The application entry point.
  * @retval int
  */intmain(void){/* USER CODE BEGIN 1 *//* USER CODE END 1 *//* MCU Configuration--------------------------------------------------------*//* Reset of all peripherals, Initializes the Flash interface and the Systick. */HAL_Init();/* USER CODE BEGIN Init *//* USER CODE END Init *//* Configure the system clock */SystemClock_Config();/* USER CODE BEGIN SysInit *//* USER CODE END SysInit *//* Initialize all configured peripherals */MX_GPIO_Init();MX_I2C1_Init();MX_USART1_UART_Init();/* USER CODE BEGIN 2 *//* USER CODE END 2 *//* Infinite loop *//* USER CODE BEGIN WHILE */while(1){//int a  = 20;/* USER CODE END WHILE */printf("Hello world!\r\n");//调用串口输出函数测试内容;//HAL_UART_Transmit (&huart1,"使用HAL库函数发送数据\n\r",40,1000);HAL_Delay(500);/* USER CODE BEGIN 3 */}/* USER CODE END 3 */}/**
  * @brief System Clock Configuration
  * @retval None
  */voidSystemClock_Config(void){
  RCC_OscInitTypeDef RCC_OscInitStruct ={0};
  RCC_ClkInitTypeDef RCC_ClkInitStruct ={0};/** Initializes the RCC Oscillators according to the specified parameters
  * in the RCC_OscInitTypeDef structure.
  */
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;
  RCC_OscInitStruct.HSIState = RCC_HSI_ON;
  RCC_OscInitStruct.HSICalibrationValue = RCC_HSICALIBRATION_DEFAULT;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_NONE;if(HAL_RCC_OscConfig(&RCC_OscInitStruct)!= HAL_OK){Error_Handler();}/** Initializes the CPU, AHB and APB buses clocks
  */
  RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
                              |RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
  RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_HSI;
  RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;if(HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_0)!= HAL_OK){Error_Handler();}}/**
  * @brief I2C1 Initialization Function
  * @param None
  * @retval None
  */staticvoidMX_I2C1_Init(void){/* USER CODE BEGIN I2C1_Init 0 *//* USER CODE END I2C1_Init 0 *//* USER CODE BEGIN I2C1_Init 1 *//* USER CODE END I2C1_Init 1 */
  hi2c1.Instance = I2C1;
  hi2c1.Init.ClockSpeed =20000;
  hi2c1.Init.DutyCycle = I2C_DUTYCYCLE_2;
  hi2c1.Init.OwnAddress1 =0;
  hi2c1.Init.AddressingMode = I2C_ADDRESSINGMODE_7BIT;
  hi2c1.Init.DualAddressMode = I2C_DUALADDRESS_DISABLE;
  hi2c1.Init.OwnAddress2 =0;
  hi2c1.Init.GeneralCallMode = I2C_GENERALCALL_DISABLE;
  hi2c1.Init.NoStretchMode = I2C_NOSTRETCH_DISABLE;if(HAL_I2C_Init(&hi2c1)!= HAL_OK){Error_Handler();}/* USER CODE BEGIN I2C1_Init 2 *//* USER CODE END I2C1_Init 2 */}/**
  * @brief USART1 Initialization Function
  * @param None
  * @retval None
  */staticvoidMX_USART1_UART_Init(void){/* USER CODE BEGIN USART1_Init 0 *//* USER CODE END USART1_Init 0 *//* USER CODE BEGIN USART1_Init 1 *//* USER CODE END USART1_Init 1 */
  huart1.Instance = USART1;
  huart1.Init.BaudRate =115200;
  huart1.Init.WordLength = UART_WORDLENGTH_8B;
  huart1.Init.StopBits = UART_STOPBITS_1;
  huart1.Init.Parity = UART_PARITY_NONE;
  huart1.Init.Mode = UART_MODE_TX_RX;
  huart1.Init.HwFlowCtl = UART_HWCONTROL_NONE;
  huart1.Init.OverSampling = UART_OVERSAMPLING_16;if(HAL_UART_Init(&huart1)!= HAL_OK){Error_Handler();}/* USER CODE BEGIN USART1_Init 2 *//* USER CODE END USART1_Init 2 */}/**
  * @brief GPIO Initialization Function
  * @param None
  * @retval None
  */staticvoidMX_GPIO_Init(void){/* GPIO Ports Clock Enable */__HAL_RCC_GPIOA_CLK_ENABLE();__HAL_RCC_GPIOB_CLK_ENABLE();}/* USER CODE BEGIN 4 *//* USER CODE END 4 *//**
  * @brief  This function is executed in case of error occurrence.
  * @retval None
  */voidError_Handler(void){/* USER CODE BEGIN Error_Handler_Debug *//* User can add his own implementation to report the HAL error return state */__disable_irq();while(1){}/* USER CODE END Error_Handler_Debug */}#ifdefUSE_FULL_ASSERT/**
  * @brief  Reports the name of the source file and the source line number
  *         where the assert_param error has occurred.
  * @param  file: pointer to the source file name
  * @param  line: assert_param error line source number
  * @retval None
  */voidassert_failed(uint8_t*file,uint32_t line){/* USER CODE BEGIN 6 *//* User can add his own implementation to report the file name and line number,
     ex: printf("Wrong parameters value: file %s on line %d\r\n", file, line) *//* USER CODE END 6 */}#endif/* USE_FULL_ASSERT */

原因分析：

重定向后的printf函数，如果没有在格式控制里面加“\r\n”就无法正确发送

例如：printf(“Hello World ! \r\n”);此条语句可以正常显示在串口助手中
printf(“Hello World !”);此条语句无法正确显示在串口助手中，而且单片机的串口TXD针脚没有发送任何数据

深入分析：

后续在阅读“The C Program Language”一书时，注意到在MS-DOS（微软的东东）环境中，文本文件是以\r\n来表示新的一行，而在UNIX/Linux中用\r表示换行，早期MacOS X的环境中用\n（现在可能已经与UNIX采用了相同的策略），意味着C在处理文本内容时，只有读到以上符号才会认为读到了“结束”符号，可以进行下一步显示操作，否则就认为没有结束，是一个不完整的数据（printf函数使用缓冲机制，会将读到的正确数据块保存到缓冲区后再进行显示）我自己理解C对于这个不完整的数据，只在缓冲区保存了一部分，没有结尾标识，故它不会把这一块数据从缓冲区送出去，因为这不是一个有效的数据，所以在USART管脚中不会发送任何数据。
上面提到了MS-DOS环境，但实际上我们使用的ARM的芯片，C的编译器和C标准都是可以设置的，具体支持用户设置到何种程度，要看IDE提供的配置项，还有一种解决办法是不使用缓冲机制，即让printf函数收到一个字符就转发一个字符，只作为一个转发作用，具体怎么实现以后再做补充

解决方案：

首先需要在main.c文件中添加以下代码

#ifdef__GNUC__#definePUTCHAR_PROTOTYPEint__io_putchar(int ch)#else#definePUTCHAR_PROTOTYPEintfputc(int ch, FILE *f)#endif
PUTCHAR_PROTOTYPE
{HAL_UART_Transmit(&huart1,(uint8_t*)&ch,1,0xFFFF);//阻塞方式打印return ch;}

注意：一定要在头文件中添加

#include"stdio.h"

否则不能使用printf函数
使用如下测试语句可以正常工作

printf("Hello world!\r\n");//调用串口输出函数测试内容;printf("%d\r\n",30);//调用串口输出函数测试内容;