初始元素不是常数？ [英] initializer element not constant?

问题描述

我是比较知道到C，只学习它的一部分发布一个卵石C / PebbleKitJS应用程序来跟踪总线。到目前为止，我有一个节点服务器上被处理的数据，我准备有一个JS文件处理的数据。但是我唯一的问题在于在C $ C $℃以内。

存储在密钥字典此code处理来自JS发送并将其分配给下面使用的变量。通过使用#define VAR 9，我可以成功有设定为9。但通过一个int VAR的。高价值，它失败并引发错误：初始元素不是常数？ 。

这是什么意思的错误，而究竟是静态的，如果我不把它定​​义常量之间的差异。显然静态瓦尔不返回任何？一些帮助将是非常美联社preciated。

更新：问题仍然是不固定的。除了初始化之一发生了以下新的错误消息。 错误：（近初始化s_data_points [0]。高'）

  INT key0_buffer;
  无效process_tuple（数组* T）
{
    //获取关键
    INT键= T-＆GT;的关键;    //获取整数值，如果present
     int值= T-＆GT;＆值 -  GT; INT32;    //获取字符串值，如果present
    焦炭STRING_VALUE [32];
    的strcpy（STRING_VALUE，T-＆GT;＆值 -  GT; CString的）;    //决定做什么
    开关（键）{
        案例KEY_0：
            //获得位置
            key0_buffer =价值;
            打破;
  }  }静态WeatherAppDataPoint s_data_points [] = {  {
 。市=圣迭戈
     .DESCRIPTION =冲浪板:)
        .icon = WEATHER_APP_ICON_GENERIC_WEATHER，
        .current = 110，
        。高= key0_buffer，
        。低= 9，
  }，
};
 

解决方案

试试这个：

 枚举{key0_buffer = 9};
 

• 在初始化的全局变量C不提供运行时间计算。 （这个概念确实存在作为称为C ++功能动态初始化。）

  执行模型是，它可以存储在ROM中的全局变量的所有字节，然后任何可修改的变量与单个的memcpy 一起复制到RAM中。分配一个全局另一个会更复杂。




• 的#define 允许你替换文本 9 ，这是一个不变的前pression。

  在使用文本替换，以避免变量作为原始的，不必要的低水平，并有可能效率低下，许多皱眉。在这种情况下，虽然，结果应该是相同的。




• 在C，枚举常量的类型 INT ，所以他们是一个合适的替代品。你的运气其他类型的，虽然。

I am relatively knew to C and only learning pieces of it to publish a Pebble C/PebbleKitJS app to track buses. So far I have the data being processed on a Node server, and I am getting ready to have the data processed by a JS File. MY one problem however lies within the C Code.

This code process data stored in a Key Dictionary sent from JS and assigns it to a variable for use below. By using #define var 9, I can successfully have the .high value set to 9. But through an int var, it fails and throws the error:initializer element not constant?? .

What does this error mean, and what exactly is the difference between static and constant if i don't define it. apparently static vars don't return anything? Some help would be much appreciated.

UPDATE: The problem still isn't fixed. The following new error message occurs in addition to the initializer one. error: (near initialization for 's_data_points[0].high')

   int key0_buffer; 


  void process_tuple(Tuple *t)
{
    //Get key
    int key = t->key;

    //Get integer value, if present
     int value = t->value->int32;

    //Get string value, if present
    char string_value[32];
    strcpy(string_value, t->value->cstring);

    //Decide what to do
    switch(key) {
        case key_0:
            //Location received
            key0_buffer = value;
            break;
  }



  }

static WeatherAppDataPoint s_data_points[] = {

  {
 .city = "San Diego",
     .description = "surfboard :)",
        .icon = WEATHER_APP_ICON_GENERIC_WEATHER,
        .current = 110,
        .high = key0_buffer,
        .low = 9,
  },   
};

解决方案

Try this instead:

enum { key0_buffer = 9 };

• C doesn't provide for runtime computations while initializing global variables. (The concept does exist as a C++ feature called "dynamic initialization.")

  The execution model is that it can store all the bytes of global variables in ROM, and then copy any modifiable variables into RAM together with a single memcpy. Assigning one global to another would be more complicated.

• #define allows you to substitute the text 9, which is a constant expression.

  Many frown upon using text substitutions to avoid variables as primitive, unnecessarily low-level, and potentially inefficient. In this case though, the results should be the same.

• In C, enum constants have type int, so they are a suitable substitute. You're out of luck for other types, though.

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