Kenhuang Academy
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      • C Undefined Behavior

      Understanding undefined behavior in C programming.

      1. Common Undefined Behaviors

      Integer Overflow

      int x = INT_MAX;
x = x + 1;  // Undefined behavior

      Array Out of Bounds

      int arr[5];
arr[5] = 10;  // Undefined behavior

      Uninitialized Variables

      int x;
printf("%d\n", x);  // Undefined behavior

      Double Free

      int *ptr = malloc(sizeof(int));
free(ptr);
free(ptr);  // Undefined behavior

      Use After Free

      int *ptr = malloc(sizeof(int));
free(ptr);
*ptr = 10;  // Undefined behavior

      2. Pointer Issues

      int *ptr = NULL;
*ptr = 10;  // Undefined behavior

int *ptr2;
*ptr2 = 10;  // Undefined behavior (uninitialized pointer)

      3. Function Return

      int func() {
    // No return statement - undefined behavior if return value is used
}

int main() {
    int x = func();  // Undefined behavior
    return 0;
}

      4. Prevention

      • Initialize all variables
      • Check array bounds
      • Validate pointers
      • Use compiler warnings
      • Use static analysis tools