1

我有个问题。在我自己的网络服务器中，我在文件范围内有以下代码：

typedef struct {
    char *slice;
    int length;
} values_index;

const char *aHeaderKeys[] = {
    /* You can add here whatever you want! */
    "Accept",
    "Accept-Charset",
    "Accept-Encoding",
    "Accept-Language",
    "Authorization",
    "Expect",
    "From",
    "Host",
    "If-Match",
    "If-Modified-Since",
    "If-None-Match",
    "If-Range",
    "If-Unmodified-Since",
    "Max-Forwards",
    "Proxy-Authorization",
    "Range",
    "Referer",
    "TE",
    "User-Agent",
    "Connection"
};

int nHeadersSizes[sizeof(aHeaderKeys) / sizeof(*aHeaderKeys)];
values_index aHeaderValuesIndexes[sizeof(aHeaderKeys) / sizeof(*aHeaderKeys)];
const int nHeadersLen = sizeof(aHeaderKeys) / sizeof(*aHeaderKeys);

但是，由于aHeaderKeys是一个由常量字符串组成的常量长度的数组，所以在程序执行过程中计算数组的长度是很愚蠢的，最好手动编写：

typedef struct {
    char *slice;
    int length;
} values_index;

const char *aHeaderKeys[20] = {
    /* You can add here whatever you want! */
    "Accept",
    "Accept-Charset",
    "Accept-Encoding",
    "Accept-Language",
    "Authorization",
    "Expect",
    "From",
    "Host",
    "If-Match",
    "If-Modified-Since",
    "If-None-Match",
    "If-Range",
    "If-Unmodified-Since",
    "Max-Forwards",
    "Proxy-Authorization",
    "Range",
    "Referer",
    "TE",
    "User-Agent",
    "Connection"
};

int nHeadersSizes[20];
values_index aHeaderValuesIndexes[20];
const int nHeadersLen = 20;

但是我的数组元素的数量在开发过程中可能会发生变化，所以每次我想添加另一个元素时，我都必须手动更改任何地方的长度。现在我的问题是：是否可以编写一个预处理器宏，如我用 JavaScript 编写的以下宏（作为伪代码）？

var aHeaders = [
    "Accept",
    "Accept-Charset",
    "Accept-Encoding",
    "Accept-Language",
    "Authorization",
    "Expect",
    "From",
    "Host",
    "If-Match",
    "If-Modified-Since",
    "If-None-Match",
    "If-Range",
    "If-Unmodified-Since",
    "Max-Forwards",
    "Proxy-Authorization",
    "Range",
    "Referer",
    "TE",
    "User-Agent",
    "Connection"
];

var sExplodedText = "const char *aHeaderKeys[" + aHeaders.length + "] = {\n\t\/* You can add here whatever you want! *\/\n\t\"" + aHeaders.join("\",\n\t\"") + "\"\n};\n\nint nHeadersSizes[" + aHeaders.length + "];\nvalues_index aHeaderValuesIndexes[" + aHeaders.length + "];\nconst int nHeadersLen = " + aHeaders.length + ";";

alert(sExplodedText);
4

2 回答 2

3

无需指定数组的大小，编译器会计算出来。你可以做

const char *aHeaderKeys[] = {
...
};


#define NR_HEADERS (sizeof aHeaderKeys/sizeof aHeaderKeys[0])

然后在需要的地方使用 NR_HEADERS。这里的表达式将由编译器在编译时计算，没有运行时计算。

于 2013-12-01T14:59:21.453 回答
0

所以，感谢@nos 和@JonasWielicki，这就是解决方案。

可以肯定的是，NR_HEADERS在以下行中

#define NR_HEADERS (sizeof aHeaderKeys / sizeof *aHeaderKeys)

将始终20 在编译时替换为，并且在以下代码中不会进行运行时计算：

const char *aHeaderKeys[] = {
    /* You can add here whatever you want! */
    "Accept",
    "Accept-Charset",
    "Accept-Encoding",
    "Accept-Language",
    "Authorization",
    "Expect",
    "From",
    "Host",
    "If-Match",
    "If-Modified-Since",
    "If-None-Match",
    "If-Range",
    "If-Unmodified-Since",
    "Max-Forwards",
    "Proxy-Authorization",
    "Range",
    "Referer",
    "TE",
    "User-Agent",
    "Connection"
};

#define NR_HEADERS (sizeof aHeaderKeys/sizeof sizeof *aHeaderKeys)

values_index aHeaderValuesIndexes[NR_HEADERS];
int nHeadersSizes[NR_HEADERS];

所以，问题解决了！

谢谢！

于 2013-12-02T01:05:12.117 回答