STM32 C++ 和重定向 std::cout 到 UART

Question

我在尝试 std::cout 使用 STM32CubeIDE（通常是标准安装的 STM32CubeIDE 的标准安装包）在 STM32 上工作时遇到问题。

为了 stdio.h 和 printf 的目的，我查阅了许多有关重定向 UART 的资源，但我正在尝试使用 std::cout 使这一切在 C++ 环境中工作。我找到的主要来源在这里：https://www.keil.com/support/man/docs/armlib/armlib_chr1358938931411.htm

根据包含 headers 的方式和时间，我会遇到不同的错误，这是我尝试过的方法：

retarget.h:

#ifndef _RETARGET_H__
#define _RETARGET_H__

#include "stm32f1xx_hal.h"
#include <sys/stat.h>
#include <stdio.h>

void RetargetInit(UART_HandleTypeDef *huart);

int _isatty(int fd);
int _write(int fd, char* ptr, int len);
int _close(int fd);
int _lseek(int fd, int ptr, int dir);
int _read(int fd, char* ptr, int len);
int _fstat(int fd, struct stat* st);


namespace std {

int fputc(int, FILE *);

}

#endif //#ifndef _RETARGET_H__

retarget.cc（剪了一点）[更正这是一个 c++ 文件]

void RetargetInit(UART_HandleTypeDef *huart) {
  gHuart = huart;

  /* Disable I/O buffering for STDOUT stream, so that
   * chars are sent out as soon as they are printed. */
  setvbuf(stdout, NULL, _IONBF, 0);
}

int _write(int fd, char* ptr, int len) {
  HAL_StatusTypeDef hstatus;

  if (fd == STDOUT_FILENO || fd == STDERR_FILENO) {
    hstatus = HAL_UART_Transmit(gHuart, (uint8_t *) ptr, len, HAL_MAX_DELAY);
    if (hstatus == HAL_OK)
      return len;
    else
      return EIO;
  }
  errno = EBADF;
  return -1;
}

namespace std {

struct __FILE
{
  int handle;
  /* Whatever you require here. If the only file you are using is */
  /* standard output using printf() for debugging, no file handling */
  /* is required. */
};
FILE __stdout;
FILE __stdin;
FILE __stderr;


int fputc(int c, FILE *stream)
{
      char tOut = c;

      return _write(STDOUT_FILENO, &tOut, 1);

  /* Your implementation of fputc(). */
}

}

和main.cpp（也剪了一点）：

#include "retarget.h"
#include <iostream>

int main(void)
{
  /* HAL Init stuff Clipped */
  RetargetInit(&huart1);
  std::cout << "\n\nSTM32 main.c Startup\n" << std::endl;

  while(1){
      std::cout << "*";

      HAL_Delay(1000);
  }
}

如果我使用 printf（将 std::cout 更改为 printf），一切正常，所以 _write 函数可以正确地发送到 UART，所以我知道大部分工作正常。

现在，关于错误。

如前所述，编译器抛出：

In file included from c:{stm32 tools path snipped}arm-none-eabi\include\c++.3.1\ext\string_conversions.h:43,
                 from c:{stm32 tools path snipped}arm-none-eabi\include\c++.3.1\bits\basic_string.h:6557,
                 from c:{stm32 tools path snipped}arm-none-eabi\include\c++.3.1\string:55,
                 from c:{stm32 tools path snipped}arm-none-eabi\include\c++.3.1\bits\locale_classes.h:40,
                 from c:{stm32 tools path snipped}arm-none-eabi\include\c++.3.1\bits\ios_base.h:41,
                 from c:{stm32 tools path snipped}arm-none-eabi\include\c++.3.1\ios:42,
                 from c:{stm32 tools path snipped}arm-none-eabi\include\c++.3.1\ostream:38,
                 from c:{stm32 tools path snipped}arm-none-eabi\include\c++.3.1\iostream:39,
                 from ../Core/Src/main.cc:26:
c:{stm32 tools path snipped}arm-none-eabi\include\c++.3.1\cstdio:111:11: error: 'int fputc(int, FILE*)' conflicts with a previous declaration
  111 |   using ::fputc;
      |           ^~~~~
In file included from ../Core/Src/main.cc:25:
../Core/Inc/retarget.h:23:5: note: previous declaration 'int std::fputc(int, FILE*)'
   23 | int fputc(int, FILE *);
      |     ^~~~~
make: *** [Core/Src/subdir.mk:41: Core/Src/main.o] Error 1

如果我翻转我的 main.cc 文件中的 include 以便首先拉入 iostream，我得到：

In file included from ../Core/Src/main.cc:26:
../Core/Inc/retarget.h:23:22: error: 'int std::fputc(int, FILE*)' conflicts with a previous declaration
   23 | int fputc(int, FILE *);
      |                      ^
In file included from c:{stm32 tools path snipped}arm-none-eabi\include\c++.3.1\cstdio:42,
                 from c:{stm32 tools path snipped}arm-none-eabi\include\c++.3.1\ext\string_conversions.h:43,
                 from c:{stm32 tools path snipped}arm-none-eabi\include\c++.3.1\bits\basic_string.h:6557,
                 from c:{stm32 tools path snipped}arm-none-eabi\include\c++.3.1\string:55,
                 from c:{stm32 tools path snipped}arm-none-eabi\include\c++.3.1\bits\locale_classes.h:40,
                 from c:{stm32 tools path snipped}arm-none-eabi\include\c++.3.1\bits\ios_base.h:41,
                 from c:{stm32 tools path snipped}arm-none-eabi\include\c++.3.1\ios:42,
                 from c:{stm32 tools path snipped}arm-none-eabi\include\c++.3.1\ostream:38,
                 from c:{stm32 tools path snipped}arm-none-eabi\include\c++.3.1\iostream:39,
                 from ../Core/Src/main.cc:25:
c:{stm32 tools path snipped}arm-none-eabi\include\stdio.h:214:5: note: previous declaration 'int fputc(int, FILE*)'
  214 | int fputc (int, FILE *);
      |     ^~~~~
make: *** [Core/Src/subdir.mk:41: Core/Src/main.o] Error 1

有什么建议吗？提前致谢。

Answer 1

终于偶然发现了解决方案，归结为 _write() 函数是如何编译的。这个函数必须用C编译器编译才能正常工作（据我所知）。

所以，解决方案，就对我有用的而言：

我将 retarget.cc 重命名回 retarget.c（它保持 retarget.c，除了 retarget.h 的包含路径外没有修改）。

对于 retarget.h 我使用了 retarget.h 的关联文件将函数原型包装在 extern "C":"

#ifndef _RETARGET_H__
#define _RETARGET_H__

#include "stm32f1xx_hal.h"
#include <sys/stat.h>
#include <stdio.h>

#ifdef __cplusplus
extern "C"
{
#endif

void RetargetInit(UART_HandleTypeDef *huart);

int _isatty(int fd);
int _write(int fd, char* ptr, int len);
int _close(int fd);
int _lseek(int fd, int ptr, int dir);
int _read(int fd, char* ptr, int len);
int _fstat(int fd, struct stat* st);

#ifdef __cplusplus
} //extern "C"
#endif

#endif //#ifndef _RETARGET_H__

现在一切正常 - std::cout << "Working now!" << std::endl;

STM32 C++ 和重定向 std::cout 到 UART

STM32 C++ and Retargeting std::cout to UART

c++

arm

stm32

iostream

cout