如何在STM32上使用Eclipse/ gcc / ac6 / sw4stm32的自定义回调来重新定位printf？

Question

我正在使用Eclipse/gcc/ac6/sw4stm32对stm32g071rb核进行编程，并且我在使用打印到SPI连接的显示器的自定义回调重新定位printf时遇到了一些困难。

现在，我的main看起来像这样：

void main(void)
{
    /* Declare BOARD typedef. */
    BOARD_TypeDef_t board;

    /* Initialize BOARD typedef. */
    board_init(&board);

    /* Initialize display */
    display_init(&board.display[displayA]);

    /* Writes a "B" to the display */
    display_write(&board.display[displayA], 0x42);
}

我想做的是在重新定位的printf中使用我的display_write功能和显示目标。

我看到的选项有：

>

使用__io_putchar函数：这可以从 syscalls.c 文件中导出。但是，它唯一需要的参数是要打印的字符，所以我不确定，也不认为我可以在那里获得BOARD_TypeDef_t。

使用写函数：这在syscall. c文件中可用。但是，我宁愿通过__io_putchar以规范的方式使用它，而不是直接编辑写函数。

使用fopencookie:我想这是我喜欢的方式，但我有一些困难。我了解到我必须激活_GNU_SOURCE并包含stdio.h，所以我在main上添加了这个:

#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#include <stdio.h> // Needed for ssize_t, cookie_io_functions_t, etc
#endif /* _GNU_SOURCE */

但是，我仍然得到一个"未知类型名称'cookie_io_functions_t'"错误，尽管这个结构是在包含的stdio. h中定义的，并且对这个stdio. h中的类型的其他调用被引用得很好，例如，cookie_write_function_t、cookie_seek_function_t等。

我不太清楚这是阿瑟gcc的问题还是Eclipse的问题，所以进展很慢。

任何关于我可能做些什么来解决这个问题的建议都是值得赞赏的。

Answer 1

我在USB CDC VCOM端口上得到了printf retargetted，将__io_putchar添加到main. c-以下代码

/* USER CODE BEGIN Header */
/**
  ******************************************************************************
  * @file           : main.c
  * @brief          : Main program body
  ******************************************************************************
  * @attention
  *
  * <h2><center>&copy; Copyright (c) 2020 STMicroelectronics.
  * All rights reserved.</center></h2>
  *
  * This software component is licensed by ST under BSD 3-Clause license,
  * the "License"; You may not use this file except in compliance with the
  * License. You may obtain a copy of the License at:
  *                        opensource.org/licenses/BSD-3-Clause
  *
  ******************************************************************************
  */
/* USER CODE END Header */

/* Includes ------------------------------------------------------------------*/
#include "main.h"
#include "usb_device.h"

/* Private includes ----------------------------------------------------------*/
/* USER CODE BEGIN Includes */
#include "usbd_cdc_if.h"
/* 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 ---------------------------------------------------------*/

/* USER CODE BEGIN PV */

/* USER CODE END PV */

/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
/* USER CODE BEGIN PFP */
int __io_putchar(int ch);
/* USER CODE END PFP */

/* Private user code ---------------------------------------------------------*/
/* USER CODE BEGIN 0 */

/* USER CODE END 0 */

/**
  * @brief  The application entry point.
  * @retval int
  */
int main(void)
{
  /* USER CODE BEGIN 1 */
    setvbuf(stdout, NULL, _IONBF, 0);
  /* 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 B                   EGIN SysInit */

  /* USER CODE END SysInit */

  /* Initialize all configured peripherals */
  MX_GPIO_Init();
  MX_USB_DEVICE_Init();
  /* USER CODE BEGIN 2 */
  HAL_Delay(5000);
//  CDC_Transmit_HS("Hello World", strlen("Hello World"));
  printf("Hello World");
  /* USER CODE END 2 */

  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  while (1)
  {
    /* USER CODE END WHILE */

    /* USER CODE BEGIN 3 */
  }
  /* USER CODE END 3 */
}

/**
  * @brief System Clock Configuration
  * @retval None
  */
void SystemClock_Config(void)
{
  RCC_OscInitTypeDef RCC_OscInitStruct = {0};
  RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};

  /** Configure the main internal regulator output voltage 
  */
  __HAL_RCC_PWR_CLK_ENABLE();
  __HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE3);
  /** Initializes the CPU, AHB and APB busses clocks 
  */
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
  RCC_OscInitStruct.HSEState = RCC_HSE_ON;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
  RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
  RCC_OscInitStruct.PLL.PLLM = 4;
  RCC_OscInitStruct.PLL.PLLN = 120;
  RCC_OscInitStruct.PLL.PLLP = RCC_PLLP_DIV2;
  RCC_OscInitStruct.PLL.PLLQ = 5;
  if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
  {
    Error_Handler();
  }
  /** Initializes the CPU, AHB and APB busses clocks 
  */
  RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
                              |RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
  RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
  RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV4;
  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV8;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV4;

  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_0) != HAL_OK)
  {
    Error_Handler();
  }
}

/**
  * @brief GPIO Initialization Function
  * @param None
  * @retval None
  */
static void MX_GPIO_Init(void)
{
  GPIO_InitTypeDef GPIO_InitStruct = {0};

  /* GPIO Ports Clock Enable */
  __HAL_RCC_GPIOC_CLK_ENABLE();
  __HAL_RCC_GPIOF_CLK_ENABLE();
  __HAL_RCC_GPIOH_CLK_ENABLE();
  __HAL_RCC_GPIOA_CLK_ENABLE();
  __HAL_RCC_GPIOB_CLK_ENABLE();
  __HAL_RCC_GPIOG_CLK_ENABLE();
  __HAL_RCC_GPIOE_CLK_ENABLE();
  __HAL_RCC_GPIOD_CLK_ENABLE();

  /*Configure GPIO pin Output Level */
  HAL_GPIO_WritePin(GPIOC, NCS_MEMS_SPI_Pin|CSX_Pin|OTG_FS_PSO_Pin, GPIO_PIN_RESET);

  /*Configure GPIO pin Output Level */
  HAL_GPIO_WritePin(ACP_RST_GPIO_Port, ACP_RST_Pin, GPIO_PIN_RESET);

  /*Configure GPIO pin Output Level */
  HAL_GPIO_WritePin(GPIOD, RDX_Pin|WRX_DCX_Pin, GPIO_PIN_RESET);

  /*Configure GPIO pin Output Level */
  HAL_GPIO_WritePin(GPIOG, LD3_Pin|LD4_Pin, GPIO_PIN_RESET);

  /*Configure GPIO pins : A0_Pin A1_Pin A2_Pin A3_Pin 
                           A4_Pin A5_Pin SDNRAS_Pin A6_Pin 
                           A7_Pin A8_Pin A9_Pin */
  GPIO_InitStruct.Pin = A0_Pin|A1_Pin|A2_Pin|A3_Pin 
                          |A4_Pin|A5_Pin|SDNRAS_Pin|A6_Pin 
                          |A7_Pin|A8_Pin|A9_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
  GPIO_InitStruct.Alternate = GPIO_AF12_FMC;
  HAL_GPIO_Init(GPIOF, &GPIO_InitStruct);

  /*Configure GPIO pins : SPI5_SCK_Pin SPI5_MISO_Pin SPI5_MOSI_Pin */
  GPIO_InitStruct.Pin = SPI5_SCK_Pin|SPI5_MISO_Pin|SPI5_MOSI_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  GPIO_InitStruct.Alternate = GPIO_AF5_SPI5;
  HAL_GPIO_Init(GPIOF, &GPIO_InitStruct);

  /*Configure GPIO pin : ENABLE_Pin */
  GPIO_InitStruct.Pin = ENABLE_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  GPIO_InitStruct.Alternate = GPIO_AF14_LTDC;
  HAL_GPIO_Init(ENABLE_GPIO_Port, &GPIO_InitStruct);

  /*Configure GPIO pin : SDNWE_Pin */
  GPIO_InitStruct.Pin = SDNWE_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
  GPIO_InitStruct.Alternate = GPIO_AF12_FMC;
  HAL_GPIO_Init(SDNWE_GPIO_Port, &GPIO_InitStruct);

  /*Configure GPIO pins : NCS_MEMS_SPI_Pin CSX_Pin OTG_FS_PSO_Pin */
  GPIO_InitStruct.Pin = NCS_MEMS_SPI_Pin|CSX_Pin|OTG_FS_PSO_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  HAL_GPIO_Init(GPIOC, &GPIO_InitStruct);

  /*Configure GPIO pins : B1_Pin MEMS_INT1_Pin MEMS_INT2_Pin TP_INT1_Pin */
  GPIO_InitStruct.Pin = B1_Pin|MEMS_INT1_Pin|MEMS_INT2_Pin|TP_INT1_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_EVT_RISING;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);

  /*Configure GPIO pins : B5_Pin VSYNC_Pin G2_Pin R4_Pin 
                           R5_Pin */
  GPIO_InitStruct.Pin = B5_Pin|VSYNC_Pin|G2_Pin|R4_Pin 
                          |R5_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  GPIO_InitStruct.Alternate = GPIO_AF14_LTDC;
  HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);

  /*Configure GPIO pin : ACP_RST_Pin */
  GPIO_InitStruct.Pin = ACP_RST_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  HAL_GPIO_Init(ACP_RST_GPIO_Port, &GPIO_InitStruct);

  /*Configure GPIO pin : OTG_FS_OC_Pin */
  GPIO_InitStruct.Pin = OTG_FS_OC_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_EVT_RISING;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  HAL_GPIO_Init(OTG_FS_OC_GPIO_Port, &GPIO_InitStruct);

  /*Configure GPIO pins : R3_Pin R6_Pin */
  GPIO_InitStruct.Pin = R3_Pin|R6_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  GPIO_InitStruct.Alternate = GPIO_AF9_LTDC;
  HAL_GPIO_Init(GPIOB, &GPIO_InitStruct);

  /*Configure GPIO pin : BOOT1_Pin */
  GPIO_InitStruct.Pin = BOOT1_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_INPUT;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  HAL_GPIO_Init(BOOT1_GPIO_Port, &GPIO_InitStruct);

  /*Configure GPIO pins : A10_Pin A11_Pin BA0_Pin BA1_Pin 
                           SDCLK_Pin SDNCAS_Pin */
  GPIO_InitStruct.Pin = A10_Pin|A11_Pin|BA0_Pin|BA1_Pin 
                          |SDCLK_Pin|SDNCAS_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
  GPIO_InitStruct.Alternate = GPIO_AF12_FMC;
  HAL_GPIO_Init(GPIOG, &GPIO_InitStruct);

  /*Configure GPIO pins : D4_Pin D5_Pin D6_Pin D7_Pin 
                           D8_Pin D9_Pin D10_Pin D11_Pin 
                           D12_Pin NBL0_Pin NBL1_Pin */
  GPIO_InitStruct.Pin = D4_Pin|D5_Pin|D6_Pin|D7_Pin 
                          |D8_Pin|D9_Pin|D10_Pin|D11_Pin 
                          |D12_Pin|NBL0_Pin|NBL1_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
  GPIO_InitStruct.Alternate = GPIO_AF12_FMC;
  HAL_GPIO_Init(GPIOE, &GPIO_InitStruct);

  /*Configure GPIO pins : G4_Pin G5_Pin B6_Pin B7_Pin */
  GPIO_InitStruct.Pin = G4_Pin|G5_Pin|B6_Pin|B7_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  GPIO_InitStruct.Alternate = GPIO_AF14_LTDC;
  HAL_GPIO_Init(GPIOB, &GPIO_InitStruct);

  /*Configure GPIO pins : D13_Pin D14_Pin D15_Pin D0_Pin 
                           D1_Pin D2_Pin D3_Pin */
  GPIO_InitStruct.Pin = D13_Pin|D14_Pin|D15_Pin|D0_Pin 
                          |D1_Pin|D2_Pin|D3_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
  GPIO_InitStruct.Alternate = GPIO_AF12_FMC;
  HAL_GPIO_Init(GPIOD, &GPIO_InitStruct);

  /*Configure GPIO pin : TE_Pin */
  GPIO_InitStruct.Pin = TE_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_INPUT;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  HAL_GPIO_Init(TE_GPIO_Port, &GPIO_InitStruct);

  /*Configure GPIO pins : RDX_Pin WRX_DCX_Pin */
  GPIO_InitStruct.Pin = RDX_Pin|WRX_DCX_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  HAL_GPIO_Init(GPIOD, &GPIO_InitStruct);

  /*Configure GPIO pins : R7_Pin DOTCLK_Pin B3_Pin */
  GPIO_InitStruct.Pin = R7_Pin|DOTCLK_Pin|B3_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  GPIO_InitStruct.Alternate = GPIO_AF14_LTDC;
  HAL_GPIO_Init(GPIOG, &GPIO_InitStruct);

  /*Configure GPIO pins : HSYNC_Pin G6_Pin R2_Pin */
  GPIO_InitStruct.Pin = HSYNC_Pin|G6_Pin|R2_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  GPIO_InitStruct.Alternate = GPIO_AF14_LTDC;
  HAL_GPIO_Init(GPIOC, &GPIO_InitStruct);

  /*Configure GPIO pin : I2C3_SDA_Pin */
  GPIO_InitStruct.Pin = I2C3_SDA_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_AF_OD;
  GPIO_InitStruct.Pull = GPIO_PULLUP;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  GPIO_InitStruct.Alternate = GPIO_AF4_I2C3;
  HAL_GPIO_Init(I2C3_SDA_GPIO_Port, &GPIO_InitStruct);

  /*Configure GPIO pin : I2C3_SCL_Pin */
  GPIO_InitStruct.Pin = I2C3_SCL_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_AF_OD;
  GPIO_InitStruct.Pull = GPIO_PULLUP;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  GPIO_InitStruct.Alternate = GPIO_AF4_I2C3;
  HAL_GPIO_Init(I2C3_SCL_GPIO_Port, &GPIO_InitStruct);

  /*Configure GPIO pins : STLINK_RX_Pin STLINK_TX_Pin */
  GPIO_InitStruct.Pin = STLINK_RX_Pin|STLINK_TX_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
  GPIO_InitStruct.Alternate = GPIO_AF7_USART1;
  HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);

  /*Configure GPIO pins : G7_Pin B2_Pin */
  GPIO_InitStruct.Pin = G7_Pin|B2_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  GPIO_InitStruct.Alternate = GPIO_AF14_LTDC;
  HAL_GPIO_Init(GPIOD, &GPIO_InitStruct);

  /*Configure GPIO pins : G3_Pin B4_Pin */
  GPIO_InitStruct.Pin = G3_Pin|B4_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  GPIO_InitStruct.Alternate = GPIO_AF9_LTDC;
  HAL_GPIO_Init(GPIOG, &GPIO_InitStruct);

  /*Configure GPIO pins : LD3_Pin LD4_Pin */
  GPIO_InitStruct.Pin = LD3_Pin|LD4_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  HAL_GPIO_Init(GPIOG, &GPIO_InitStruct);

  /*Configure GPIO pins : SDCKE1_Pin SDNE1_Pin */
  GPIO_InitStruct.Pin = SDCKE1_Pin|SDNE1_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
  GPIO_InitStruct.Alternate = GPIO_AF12_FMC;
  HAL_GPIO_Init(GPIOB, &GPIO_InitStruct);

}

/* USER CODE BEGIN 4 */
int __io_putchar(int ch) {
    CDC_Transmit_HS(&ch, 1);
    return ch;
}
/* USER CODE END 4 */

/**
  * @brief  This function is executed in case of error occurrence.
  * @retval None
  */
void Error_Handler(void)
{
  /* USER CODE BEGIN Error_Handler_Debug */
  /* User can add his own implementation to report the HAL error return state */

  /* USER CODE END Error_Handler_Debug */
}

#ifdef  USE_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
  */
void assert_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,
     tex: printf("Wrong parameters value: file %s on line %d\r\n", file, line) */
  /* USER CODE END 6 */
}
#endif /* USE_FULL_ASSERT */

/************************ (C) COPYRIGHT STMicroelectronics *****END OF FILE****/

Answer 2

经过一番调查，我找到了一个可行的解决方案。

这里有完整的帖子，包括最终产品的图片：https://zfembedded.wordpress.com/2020/02/27/redirecting-printf-on-stm32-using-fopencookie/

从在屏幕上打印“B”的基本程序开始，我执行了以下操作：

1. fopencookie函数位于stdio中。h，所以这需要包括在内
2. 为了激活它，必须在包含之前定义_GNU_SOURCE
3. 我们为显示器创建一个流my_stream0。我们也可以为stdout创建一个
4. fopencookie函数需要cookie_io_functions，所以我们定义了它们。这些似乎不参与行动，但没有它们，事情对我来说就不起作用。关于为什么会这样的提示很有帮助
5. 我们为cookie_io_functions的一个组件编写函数，在本例中为.write。对我来说，这个函数不需要做任何事情
6. 我们编写流写入函数
7. 我们将流写入函数和板定义传递给定义的流
8. 我们修改流的缓冲
9. 我们测试了所创建流的fprintfs和printf

'

/* 2 */
#define _GNU_SOURCE

/* 1 */
#include <stdio.h>

/* 5 */
static ssize_t dummy_cookie_write(void *c, const char *buf, size_t size)
{
   return size;
}

/* 6 */
int displayA_stream_write(struct _reent *q1, void *q2, const char *q3, int q4)
{
    (void)q1;
    BOARD_TypeDef_t* q5 = (BOARD_TypeDef_t*)q2;

    int DataIdx;

    for (DataIdx = 0; DataIdx < q4; DataIdx++)
    {
        display_write(&q5->display[displayA], *q3++);
    }

    return q4;
}

void main(void)
{
    /* Declare BOARD typedef. */
    BOARD_TypeDef_t board;

    /* Initialize BOARD typedef. */
    board_init(&board);

    /* Initialize display */
    display_init(&board.display[displayA]);

    /* Writes a "B" to the display */
    display_write(&board.display[displayA], 0x42);

    /* 4 */
    cookie_io_functions_t dummy_cookie_funcs = {
            .read  = 0,
            .write = dummy_cookie_write, /* Setting this to 0 breaks the solution. */
            .seek  = 0,
            .close = 0
        };

    /* 3 */
    FILE *my_stream0 = fopencookie(NULL,"w", dummy_cookie_funcs); /* Replacing dummy_cookie_funcs with NULL breaks the solution. */
    stdout = fopencookie(NULL,"w", dummy_cookie_funcs);

    /* 8 */
    setbuf(my_stream0, NULL);
    setbuf(stdout, NULL);

    /* 7 */
    my_stream0->_write = displayA_stream_write;
    my_stream0->_cookie = (void *)&board;
    stdout->_write = displayA_stream_write;
    stdout->_cookie = (void *)&board;

    /* 9 */
    fprintf(my_stream0, "\nNowhere");
    fprintf(stdout, "\nSomewhere");
    printf("\nHere");

}

'

使这一切成为可能的关键发现是发现#7写入比#4写入更重要。

谢谢你的建议。