我們在寫代碼的時候總是被領(lǐng)導(dǎo)告知 慎用sprintf函數(shù) ，這個函數(shù)占用CPU時間較多，對于字符串拼接可以使用strcat函數(shù)替代（并未所有情形都可替代）。

可是艾兔還是好奇，這倆函數(shù)在耗時上到底有多大區(qū)別呢？

今天艾兔就親身測試一下。

為了易于分析，艾兔分別用sprintf和strcat、strcpy函數(shù)分別打印300個字符循環(huán)100次。然后利用單片機(jī)定時器計算三者的耗時。

下面是驗(yàn)證代碼和結(jié)果。

while(1)里面進(jìn)行計時并打印：

int main(void)
{
  /* USER CODE BEGIN 1 */
  /* USER CODE END 1 */
  /* MCU Configuration----------------------------------------------------------*/
  /* Reset of all peripherals, Initializes the Flash interface and the Systick. */
  HAL_Init();
  /* Configure the system clock */
  SystemClock_Config();
  /* Initialize all configured peripherals */
  MX_GPIO_Init();
  MX_USART3_UART_Init();
  MX_TIM1_Init();
  /* USER CODE BEGIN 2 */
  /* USER CODE END 2 */
  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  //WifiValue.WifiBreathingMode = 0xFF;
    int Count = 0;
    char buf[1000] = {0};
    while (1)
    {
    Time1_AtWifiReilDataSend_Ms = 0;
    for(Count = 0; Count < 100; Count++)
    {
      //300個字符
      sprintf(buf,"%s","AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAn");      
      buf[0] = 0;
    }
    printf("sprintf = %d msn",Time1_AtWifiReilDataSend_Ms);


    Time1_AtWifiReilDataSend_Ms = 0;
    for(Count = 0; Count < 100; Count++)
    {
      //300個
      strcat(buf,"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAn");
      buf[0] = 0;
    }  
    printf("strcat = %d msn",Time1_AtWifiReilDataSend_Ms);


    Time1_AtWifiReilDataSend_Ms = 0;
    for(Count = 0; Count < 100; Count++)
    {
      //300個
      strcpy(buf,"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAn");
      buf[0] = 0;
    }  
    printf("strcpy = %d msn",Time1_AtWifiReilDataSend_Ms);      
    while(1);


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


}

啟動定時器，每1ms進(jìn)入中斷一次：

//定時器1中斷回調(diào)處理函數(shù)
uint16_t Time1_AtWifiReilDataSend_Ms = 0;
void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef *htim)
{
    if(htim- >Instance == htim1.Instance)
    {
    Time1_AtWifiReilDataSend_Ms++;  
    }
}

測試結(jié)果：

**sprintf = 38 ms **

**strcat = 7 ms **

**strcpy = 7 ms **

結(jié)果表明分別 打印30000個字符 ，sprintf函數(shù)耗時是strcat和strcpy函數(shù)的5.43倍。

我們修改發(fā)送字符數(shù)進(jìn)行進(jìn)一步驗(yàn)證：

我們測試50次循環(huán)循環(huán)，看看15000個字符的耗時對比。

while (1)
    {
    Time1_AtWifiReilDataSend_Ms = 0;
    for(Count = 0; Count < 50; Count++)
    {
      //300個字符
      sprintf(buf,"%s","AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAn");      
      buf[0] = 0;
    }
    printf("sprintf = %d ms ",Time1_AtWifiReilDataSend_Ms);

    Time1_AtWifiReilDataSend_Ms = 0;
    for(Count = 0; Count < 50; Count++)
    {
      //300個
      strcat(buf,"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAn");
      buf[0] = 0;
    }  
    printf("strcat = %d ms ",Time1_AtWifiReilDataSend_Ms);

    Time1_AtWifiReilDataSend_Ms = 0;
    for(Count = 0; Count < 50; Count++)
    {
      //300個
      strcpy(buf,"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAn");
      buf[0] = 0;
    }  
    printf("strcpy = %d ms ",Time1_AtWifiReilDataSend_Ms);    
    while(1);

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

**sprintf = 19 ms **

**strcat = 4 ms **

**strcpy = 3 ms **

結(jié)果表明分別 打印15000個字符 ，sprintf函數(shù)耗時是strcat和strcpy函數(shù)的4.75倍。

** 我們繼續(xù)測試10次循環(huán)循環(huán)，看看3000個字符的耗時對比。**

while (1)
    {
    Time1_AtWifiReilDataSend_Ms = 0;
    for(Count = 0; Count < 10; Count++)
    {
      //300個字符
      sprintf(buf,"%s","AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAn");      
      buf[0] = 0;
    }
    printf("sprintf = %d ms ",Time1_AtWifiReilDataSend_Ms);

    Time1_AtWifiReilDataSend_Ms = 0;
    for(Count = 0; Count < 10; Count++)
    {
      //300個
      strcat(buf,"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAn");
      buf[0] = 0;
    }  
    printf("strcat = %d ms ",Time1_AtWifiReilDataSend_Ms);

    Time1_AtWifiReilDataSend_Ms = 0;
    for(Count = 0; Count < 10; Count++)
    {
      //300個
      strcpy(buf,"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAn");
      buf[0] = 0;
    }  
    printf("strcpy = %d ms ",Time1_AtWifiReilDataSend_Ms);    
    while(1);

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

**sprintf = 4ms **

**strcat = 1 ms **

**strcpy = 1 ms **

結(jié)果表明分別打印3000個字符 ，sprintf函數(shù)耗時是strcat和strcpy函數(shù)的4倍。

結(jié)論：

因此在程序使用中如果只是對很少字符串進(jìn)行操作，比如幾十個，用哪個函數(shù)差別不大，但是如果對幾百個字符、甚至上個字符的組包還是要考慮一下的。