多行註釋不能巢狀

在 C 中，多行註釋/ *和* /不巢狀。

如果使用這種註釋方式註釋程式碼塊或函式塊：

/*
 * max(): Finds the largest integer in an array and returns it.
 * If the array length is less than 1, the result is undefined.
 * arr: The array of integers to search.
 * num: The number of integers in arr.
 */
int max(int arr[], int num)
{
    int max = arr[0];
    for (int i = 0; i < num; i++)
        if (arr[i] > max)
            max = arr[i];
    return max;
}

你將無法輕易評論出來：

//Trying to comment out the block...
/*

/*
 * max(): Finds the largest integer in an array and returns it.
 * If the array length is less than 1, the result is undefined.
 * arr: The array of integers to search.
 * num: The number of integers in arr.
 */
int max(int arr[], int num)
{
    int max = arr[0];
    for (int i = 0; i < num; i++)
        if (arr[i] > max)
            max = arr[i];
    return max;
}

//Causes an error on the line below...
*/

一種解決方案是使用 C99 樣式註釋：

// max(): Finds the largest integer in an array and returns it.
// If the array length is less than 1, the result is undefined.
// arr: The array of integers to search.
// num: The number of integers in arr.
int max(int arr[], int num)
{
    int max = arr[0];
    for (int i = 0; i < num; i++)
        if (arr[i] > max)
            max = arr[i];
    return max;
}

現在可以輕鬆地註釋掉整個塊：

/*

// max(): Finds the largest integer in an array and returns it.
// If the array length is less than 1, the result is undefined.
// arr: The array of integers to search.
// num: The number of integers in arr.
int max(int arr[], int num)
{
    int max = arr[0];
    for (int i = 0; i < num; i++)
        if (arr[i] > max)
            max = arr[i];
    return max;
}

*/

另一種解決方案是避免使用註釋語法禁用程式碼，而是使用 #ifdef 或 #ifndef 前處理器指令。這些指令可以巢狀，讓你可以自由地以你喜歡的樣式註釋程式碼。

#define DISABLE_MAX /* Remove or comment this line to enable max() code block */

#ifdef DISABLE_MAX
/*
 * max(): Finds the largest integer in an array and returns it.
 * If the array length is less than 1, the result is undefined.
 * arr: The array of integers to search.
 * num: The number of integers in arr.
 */
int max(int arr[], int num)
{
    int max = arr[0];
    for (int i = 0; i < num; i++)
        if (arr[i] > max)
            max = arr[i];
    return max;
}
#endif

一些導遊走那麼遠，建議程式碼段必須永遠不會被註釋掉的，如果程式碼是要暫時停用一個可以訴諸使用 #if 0 指令。

請參閱 #if 0 以阻止程式碼部分 。