在STM32工程中调用printf函数，需要加入如下代码：

1. <div align="left">#ifdef __GNUC__     
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2.   /* With GCC/RAISONANCE, small printf (option LD Linker->Libraries->Small printf
   
3.      set to 'Yes') calls __io_putchar() */
   
4.   #define PUTCHAR_PROTOTYPE int __io_putchar(int ch)
   
5. #else
   
6.   #define PCHAR_PROTOTYPE int fputc(int ch, FILE *f)
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7. #endif /* __GNUC__ UT*/
   
8. </div><div align="left">void Printf_Init(void)
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9. {
   
10.   /*!< At this stage the microcontroller clock setting is already configured,
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11.        this is done through SystemInit() function which is called from startup
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12.        file (startup_stm32f10x_xx.s) before to branch to application main.
    
13.        To reconfigure the default setting of SystemInit() function, refer to
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14.        system_stm32f10x.c file
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15.      */     
    
16.       
    
17.   /* USARTx configured as follow:
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18.         - BaudRate = 115200 baud  
    
19.         - Word Length = 8 Bits
    
20.         - One Stop Bit
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21.         - No parity
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22.         - Hardware flow control disabled (RTS and CTS signals)
    
23.         - Receive and transmit enabled
    
24.   */
    
25.   USART_InitStructure.USART_BaudRate = 115200;
    
26.   USART_InitStructure.USART_WordLength = USART_WordLength_8b;
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27.   USART_InitStructure.USART_StopBits = USART_StopBits_1;
    
28.   USART_InitStructure.USART_Parity = USART_Parity_No;
    
29.   USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;
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30.   USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx;
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31. 
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32.   STM_EVAL_COMInit(COM1, &USART_InitStructure);
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33. 
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34.   /* Output a message on Hyperterminal using printf function */
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35.   //printf("\n\rUSART Printf Example: retarget the C library printf function to the USART\n\r");<div align="left">//  printf("\r\n\n\n <a href="http://WWW.ARMJISHU.COM" target="_blank">WWW.ARMJISHU.COM</a>  %s configured....", EVAL_COM1_STR);</div><div align="left">//  printf("\n\r ############ <a href="http://WWW.ARMJISHU.COM" target="_blank">WWW.ARMJISHU.COM</a>! ############ ("__DATE__ " - " __TIME__ ")\n\r");</div>}
    
36. 
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37. /**
    
38.   * @brief  Retargets the C library printf function to the USART.
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39.   * @param  None
    
40.   * @retval None
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41.   */
    
42. PUTCHAR_PROTOTYPE
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43. {
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44.   /* Place your implementation of fputc here */
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45.   /* e.g. write a character to the USART */
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46.   USART_SendData(EVAL_COM1, (uint8_t) ch);
    
47. 
    
48.   /* Loop until the end of transmission */
    
49.   while (USART_GetFlagStatus(EVAL_COM1, USART_FLAG_TC) == RESET)
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50.   {}
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51. 
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52.   return ch;
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53. }</div>
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