c++ - 宏需要一个表达式

Question

我目前正在做一个学校项目，我正在做的部分作业的要求如下所示:

The error state which the client can reference to determine if the object holds a valid date, and if not, which part of the date is in error. The possible error states are integer values defined as macros in the Date class header:

NO_ERROR   0  -- No error - the date is valid
CIN_FAILED 1  -- istream failed on information entry
YEAR_ERROR 2  -- Year value is invalid
MON_ERROR  3  -- Month value is invalid
DAY_ERROR  4  -- Day value is invalid"

和:

void errCode(int errorCode);

This function sets the error state variable to one of the values listed above.

但是，当我将代码放入第二个函数时，当我尝试在 if 语句中使用宏值时，visual studio 给我一条红色下划线并指出“需要一个表达式”。

// this code is unfinished and partial

void Date::errCode(int errorCode)
{
    if (errorCode == NO_ERROR) // <- red underline here
    {
        m_errorState = NO_ERROR; // <- red underline here
    }
    if (errorCode == 1)
    {
    }
}

头文件定义如下:

#define NO_ERROR = 0        // No error - the date is valid
#define CIN_FAILED = 1      // istream failed on information entry
#define YEAR_ERROR = 2      // Year value is invalid
#define MON_ERROR = 3       // Month value is invalid
#define DAY_ERROR = 4       // Day value is invalid

Answer 1

宏不需要 = 运算符，因为它们会被您为它们定义的任何内容替换。在您的情况下，errorCode == NO_ERROR 将等同于 errorCode == = 0 而不是您可能期望的 errorCode == 0。

只需去掉等号:

#define NO_ERROR 0        // No error - the date is valid
#define CIN_FAILED 1      // istream failed on information entry
#define YEAR_ERROR 2      // Year value is invalid
#define MON_ERROR 3       // Month value is invalid
#define DAY_ERROR 4       // Day value is invalid