Question

尝试在C ++程序上调试EXEC_BAD_ACCESS错误。程序将作为输入数字转换为字符串。然后我想返回生成最大可能数的整数的排序。

主要是

int main() {
  // Number of ints to input
  int n;
  std::cin >> n;
  vector<string> a(n);
  // Input numbers as strings
  for (size_t i = 0; i < a.size(); i++) {
    std::cin >> a[i];
  }
  std::sort(a.begin(), a.end(), is_greater_than_or_equal);
  std::cout << largest_number(a);
  std::cout << std::endl;
  return 0;
}

使用lldb，看起来错误来自sort / is_greater_than_or_equal函数。

is_greater_than_or_equal是

bool is_greater_than_or_equal(string n1, string n2) {
  int l1 = n1.length();
  int l2 = n2.length();
  int min = (l1 < l2) ? l1 : l2;
  for (int i = 0; i < min; i++) {
    // First digit is strictly larger
    if (n1[i] > n2[i]) {
      return true;
      // First digit is strictly lower
    } else if (n1[i] < n2[i]) {
      return false;
      // First digits are the same
    } else {
      // If first is single digit
      if (l1 == 1) {
        return true;
        // If the second is single digit
      } else if (l2 == 1) {
        return false;
        // If they're both multiple digits
      } else {
        int j = i + 1;
        // Keep checking until hitting min
        while (j < min) {
          if (n1[j] > n2[j]) {
            return true;
          } else if (n1[j] < n2[j]) {
            return false;
          } else {
            j++;
          }
        }
        // If min was hit and nothing was returned
        // choose integer with lowest length
        if (l1 > l2) {
          return false;
        }
        return true;
      }
    }
  }
  return false;
}

使用lldb检查后，似乎sort函数继续经过a.end() - 我相信这是导致错误的原因，但我不确定为什么会发生这种情况。原因是检查对is_greater_than_or_equal的调用会显示类似

的调用

(lldb) fr v
(std::__1::string) n1 = "9"
(std::__1::string) n2 = "2"
(int) l1 = 0
(int) l2 = 0
(int) min = 0

起初然后，过了一会儿，他们就变成了

(lldb) fr v
(std::__1::string) n1 = ""
(std::__1::string) n2 = ""
(int) l1 = 0
(int) l2 = 0
(int) min = 0

显然不应该发生（顺便说一句，我在分配l1和l2之前设置了断点，这就是长度不匹配的原因 - 这个点实际上只是看n1和n2）。

lldb的输出是

(lldb) r
Process 7405 launched: '/Users/etc' (x86_64)
100
2 8 2 3 6 4 1 1 10 6 3 3 6 1 3 8 4 6 1 10 8 4 10 4 1 3 2 3 2 6 1 5 2 9 8 5 10 8 7 9 6 4 2 6 3 8 8 9 8 2 9 10 3 10 7 5 7 1 7 5 1 4 7 6 1 10 5 4 8 4 2 7 8 1 1 7 4 1 1 9 8 6 5 9 9 3 7 6 3 10 8 10 7 2 5 1 1 9 9 5
Process 7405 stopped
* thread #1: tid = 0x2f2a6, 0x00007fff97c82051 libsystem_platform.dylib`_platform_memmove$VARIANT$Ivybridge + 49, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x0)
    frame #0: 0x00007fff97c82051 libsystem_platform.dylib`_platform_memmove$VARIANT$Ivybridge + 49
libsystem_platform.dylib`_platform_memmove$VARIANT$Ivybridge:
->  0x7fff97c82051 <+49>: rep    
    0x7fff97c82052 <+50>: movsb  (%rsi), %es:(%rdi)
    0x7fff97c82053 <+51>: popq   %rbp
    0x7fff97c82054 <+52>: retq

我不确定如何解释这个输出，也不完全清楚这种内部运作方式。

C ++中LLDB上的EXC_BAD_ACCESS错误

0 个答案: