[英]A way to automatically cast string literals to `unsigned char*` in C?
I'm using libxml2 for a project, and one of its quirks is that xmlChar
is a typedef for unsigned char
instead of just char
. 我正在为项目使用libxml2,它的一个怪癖是
xmlChar
是unsigned char
的typedef,而不仅仅是char
。 As far as I can tell, that doesn't have any effect on the actual execution, but it makes it really annoying to use string literals since I have to manually cast to const xmlChar*
. 据我所知,这对实际执行没有任何影响,但是使用字符串文字确实很烦人,因为我必须手动将其转换为
const xmlChar*
。 All I really want is to be able to write xmlGetProp(node, "some-property")
instead of xmlGetProp(node, (const xmlChar*)"some-property")
. 我真正想要的是能够编写
xmlGetProp(node, "some-property")
而不是xmlGetProp(node, (const xmlChar*)"some-property")
。 It may seem minor, but it makes the code significantly harder to read when every other statement has a (const xmlChar*)
cast. 它可能看起来很小,但是当其他每个语句都具有
(const xmlChar*)
时,它会使代码变得更加难以阅读。
Is there a way to make const char*
cast to const xmlChar*
( const unsigned char*
) without manual casts? 有没有一种方法可以将
const char*
强制转换为const xmlChar*
( const unsigned char*
)而无需手动强制转换? Or alternately, is there a reason I shouldn't do this? 或者,是否有我不应该这样做的原因?
I assume this would be reasonably easy in C++, but I'm stuck with C. 我认为这在C ++中会相当容易,但是我对C感到困惑。
Issues with char *
and unsigned char *
are annoying , because (on 2's complement) they all point to the same thing. char *
和unsigned char *
很烦人,因为(在2的补码上)它们都指向同一件事。 Even though aliasing via these types is permitted, the C standard requires a diagnostic. 即使允许通过这些类型进行别名,C标准也需要进行诊断。 Some compilers have an option to suppress diagnostic for this case (when you omit the cast).
一些编译器有一个选项可以抑制这种情况的诊断(当您省略强制转换时)。
You could write some wrappers: 您可以编写一些包装器:
xmlChar *VxmlGetProp(const xmlNode *node, const char *name)
{
return xmlGetProp(node, (const unsigned char *)name);
}
Note that I didn't write const xmlChar
in the cast as this would silently cause broken behaviour if you later reconfigured libxml to use wide characters for xmlChar
. 请注意,我没有在类型转换中编写
const xmlChar
,因为如果您稍后将libxml重新配置为对xmlChar
使用宽字符,这将无提示地导致行为中断。
You could even use const void *
as the argument type to allow your function to take both const char *
, and const unsigned char *
. 您甚至可以使用
const void *
作为参数类型,以允许您的函数同时使用const char *
和const unsigned char *
。
Another option (which also adds some typo-resistance) to your code would be to not use the string literals in place; 您的代码中的另一种选择(这也增加了抗错字性)是不使用字符串文字。 instead have them in a table, eg
而是将它们放在表格中,例如
#define STRING_FOOBAR ((const unsigned char *)"foobar")
and then use STRING_FOOBAR
in your code. 然后在您的代码中使用
STRING_FOOBAR
。
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