[英]How do I convert a NSString into a std::string?
I have an NSString
object and want to convert it into a std::string
. 我有一个NSString
对象,并希望将其转换为std::string
。
How do I do this in Objective-C++? 我如何在Objective-C ++中执行此操作?
NSString *foo = @"Foo";
std::string bar = std::string([foo UTF8String]);
Edit: After a few years, let me expand on this answer. 编辑:几年后,让我扩展这个答案。 As rightfully pointed out, you'll most likely want to use cStringUsingEncoding:
with NSASCIIStringEncoding
if you are going to end up using std::string
. 正如所指出的那样,如果你最终要使用std::string
,你最有可能想要使用cStringUsingEncoding:
使用NSASCIIStringEncoding
。 You can use UTF-8 with normal std::strings
, but keep in mind that those operate on bytes and not on characters or even graphemes. 您可以将UTF-8与普通的std::strings
,但请记住,这些操作是基于字节而不是字符甚至是字形。 For a good "getting started", check out this question and its answer . 要获得良好的“入门”,请查看此问题及其答案 。
Also note, if you have a string that can't be represented as ASCII but you still want it in an std::string
and you don't want non-ASCII characters in there, you can use dataUsingEncoding:allowLossyConversion:
to get an NSData
representation of the string with lossy encoded ASCII content, and then throw that at your std::string
另请注意,如果您的字符串不能表示为ASCII但仍然需要它在std::string
并且您不希望其中包含非ASCII字符,则可以使用dataUsingEncoding:allowLossyConversion:
获取具有有损编码的ASCII内容的字符串的NSData
表示,然后将其抛出到std::string
As Ynau's suggested in the comment, in a general case it would be better to keep everything on the stack instead of heap (using new
creates the string on the heap), hence (assuming UTF8 encoding): 正如Ynau在评论中所建议的那样,在一般情况下,最好将所有内容保存在堆栈而不是堆中(使用new
在堆上创建字符串),因此(假设UTF8编码):
NSString *foo = @"Foo";
std::string bar([foo UTF8String]);
As noted on philjordan.eu it could also be that the NSString is nil
. 如philjordan.eu所述 ,也可能是NSString nil
。 In such a case the cast should be done like this: 在这种情况下,演员应该这样做:
// NOTE: if foo is nil this will produce an empty C++ string //注意:如果foo为nil,这将产生一个空的C ++字符串
// instead of dereferencing the NULL pointer from UTF8String. //而不是从UTF8String中取消引用NULL指针。
This would lead you to such a conversion: 这将导致您进行这样的转换:
NSString *foo = @"Foo";
std::string bar = std::string([foo UTF8String], [foo lengthOfBytesUsingEncoding:NSUTF8StringEncoding]);
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