Question

我在某些设备上进行编程，但遇到了相当奇怪的情况。同一个变量 - 第一次具有正确的值，但是代码中不同位置的SAME变量，具有不同的值。是什么导致这个？我很确定我没有修改介于两者之间的变量，我也很确定我没有不小心使用一些指针修改变量。

导致这种情况的原因是什么？我真的很困惑？与我有关，例如我使用整个可用堆栈一些函数的空间 - 并且由于这个编译器自动 0-ifies我的变量（或类似的东西）？我在单个函数f中有一些长代码。

以下是我的代码中使用pointsEntered变量的详细信息（如何使用）。

  /* Let the user input points */

  s32 pointsEntered = 0;
  int pointsCounter = 0;
  while(1)
  {

     if(pointsCounter == 3)
       return; // User entered wrong points 3 times, exit function

     bool retStatus = false;
     retStatus = inputPoints(&pointsEntered);

     if(false == retStatus) // If user didn't enter amount, exit this function
       return;

     if(pointsEntered>atoi(userAmount)){
          PromptBox(false, 0, "Points should not be more\n than current points");
       pointsCounter++;  
       continue;
     }
     break;

 }

// PROBLEM: pointsEntered  - is OK here but as it will be shown below, it gets modified down the way
// even though I don't change it directly

  char intTest1[50];
  sprintf(intTest1, "1pentered %d", pointsEntered); // Here the value is OK! It shows value that I entered, e.g., 220
  PromptBox(false, 0, intTest1);  



  /* Let the user enter 4 digit pin code */
  u8 pinEntered[5] = {0};
  bool retStatus1 = false;
  retStatus1 = inputPin(pinEntered);
  pinEntered[5]='\0';
  if(false == retStatus1) // If user didn't enter amount, exit this function
     return;

  char intTest2[50];
  sprintf(intTest2, "2pentered %d", pointsEntered); // Here pointsEnetered is OK
  PromptBox(false, 0, intTest2); 


  /* Compute hash of pin code*/
  s32 siRet1 = 0;
  u8 pinVerify[25]={0};
  u8 hashResult[16] = {0};
  memcpy(pinVerify,pinEntered,4);
  memcpy(&pinVerify[4],"XXXX",21);
  siRet1 = sdkMD5(hashResult,pinVerify,25);

  char intTest3[50];
  sprintf(intTest3, "3pentered %d", pointsEntered); // Here pointsEntered has changed!!!
   PromptBox(false, 0, intTest3); 

  /* convert string hash code to byte array */
  unsigned char val[16] = {0};
  unsigned char * pos = pinHash;
  size_t count = 0;
  // WARNING: no sanitization or error-checking whatsoever 
  for(count = 0; count < sizeof(val)/sizeof(val[0]); count++) 
  {
     sscanf(pos, "%2hhx", &val[count]);
     pos += 2 * sizeof(char);
  }

  char intTest4[50];
  sprintf(intTest4, "4pentered %d", pointsEntered);
  PromptBox(false, 0, intTest4); 

  /* Does the pin hash match ? */
  if (siRet == SDK_OK && (!memcmp(hashResult,val,16)))
  {
    MsgBox("PIN OK","",0,SDK_KEY_MASK_ESC | SDK_KEY_MASK_ENTER);
  }
  else
  {
    MsgBox("PIN doesn't match-exiting","",0,SDK_KEY_MASK_ESC | SDK_KEY_MASK_ENTER);
    return;

  }

  char intTest[50];
  sprintf(intTest, "pentered %d", pointsEntered);
  PromptBox(false, 0, intTest);

Answer 1

这两行可能会导致它（因为它是未定义的行为）：

u8 pinEntered[5] = {0};
...
pinEntered[5]='\0';

在这里，您声明一个包含五个条目的数组，然后分配给第六个项。这很可能会覆盖堆栈中的任何先前变量。

遇到奇怪的情况 - 变量值

1 个答案: