How do C++ functions handle errors gracefully?

Techniques for handling errors in C functions include: exception handling, noexcept specification, return error code, standard return value and custom exception. Exception handling provides a reliable means of catching and handling errors, and the noexcept specification indicates that functions will not throw exceptions. By returning an error code or enumeration value, the caller can check the error status. In some cases, standard return values ​​such as nullptr are used to indicate errors. For custom errors, exception classes can be defined to provide more specific information.

Tips for gracefully handling errors in C functions

When writing robust code in C, handle errors gracefully to It's important. By employing the following techniques, you can ensure that your functions continue to work properly when errors are encountered.

1. Exception handling

Using try-catch blocks to catch and handle errors is a common method. You can specify the types of errors to catch and provide an error handler to handle them.

try {
  // 代码可能抛出异常的地方
} catch (const std::exception& e) {
  // 处理错误
}

2. noexcept Specification

If you are sure that the function will not throw any exceptions, you can use the noexcept specification . This will tell the compiler that the function will not throw an exception and allow certain optimizations to be done.

int safe_function() noexcept {
  // 函数保证不会抛出异常
}

3. Return error code

Another way to handle errors is to return an error code or enumeration value. Callers can check this value to determine whether the function executed successfully and any errors that occurred.

enum class ErrorCodes {
  Success,
  InvalidInput,
  IOError
};

ErrorCodes do_something() {
  // 函数执行并返回错误码
}

4. Standard return values

For some situations, it may be appropriate to use standard return values ​​to indicate errors. For example, in a find operation, a nullptr can be returned to indicate that the item was not found.

Item* find_item(const std::string& name) {
  // 函数返回一个指针，指向找到的项目，或 nullptr 如果未找到
}

5. Custom exceptions

For complex or custom errors, you can define a custom exception class. This allows you to provide more specific information about the error and simplify error handling.

class MyException : public std::exception {
public:
  MyException(const std::string& message) : message_(message) {}
  const char* what() const noexcept override { return message_.c_str(); }

private:
  std::string message_;
};

Practical case:

Consider a function that reads numbers from a file. This function may throw an exception if the file does not exist or the data format is invalid. We can also use error codes to indicate other errors, such as file corruption or access denied.

#include <fstream>
#include <stdexcept>

using namespace std;

enum class ErrorCodes {
  Success,
  FileNotFound,
  InvalidDataFormat,
  FileAccessDenied
};

int read_number_from_file(const string& filename) {
  ifstream file(filename);
  if (!file.is_open()) {
    return ErrorCodes::FileNotFound;
  }

  int number;
  file >> number;
  if (file.fail()) {
    return ErrorCodes::InvalidDataFormat;
  }

  return number;
}

When calling this function, the caller can check the error code returned to determine whether the number was successfully read, and any errors that occurred. This allows the caller to take appropriate action based on the error.

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