首先将串口初始化，然后添加重定向代码
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下面使用的是串口三，因此以串口三为例：

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1. UART_HandleTypeDef huart3;
   
2. #ifdef __GNUC__
   
3. /* With GCC/RAISONANCE, small printf (option LD Linker->Libraries->Small printf
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4. set to 'Yes') calls __io_putchar() */
   
5. #define PUTCHAR_PROTOTYPE int __io_putchar(int ch)
   
6. #else
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7. #define PUTCHAR_PROTOTYPE int fputc(int ch, FILE *f)
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8. #endif /* __GNUC__ */
   
9. /**
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10. * @brief Retargets the C library printf function to the USART.
    
11. * @param None
    
12. * @retval None
    
13. */
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14. PUTCHAR_PROTOTYPE
    
15. {
    
16.   /* Place your implementation of fputc here */
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17.   /* e.g. write a character to the EVAL_COM1 and Loop until the end of transmission */
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18.   HAL_UART_Transmit(&huart3, (uint8_t *)&ch, 1, 0x0001);
    
19.   return ch;
    
20. }

复制代码

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添加完代码后就可以使用printf进行打印了~
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