一 NSString 转 char *

1. UTF8String

const char *cString = [string UTF8String];

2. cStringUsingEncoding:

const char *cString = [string cStringUsingEncoding:NSUTF8StringEncoding];

3. getCString:maxLength:encoding:

char cStringPtr[string.length * 3 + 1];
memset(cStringPtr, 0, sizeof(cStringPtr));
[string getCString:cStringPtr maxLength:sizeof(cStringPtr) encoding:NSUTF8StringEncoding];

UTF8编码需要占用3个字节，因此这里需要*3。

- (BOOL)getCString:(char *)buffer maxLength:(NSUInteger)maxBufferCount encoding:(NSStringEncoding)encoding;
// NO return if conversion not possible due to encoding errors or too small of a buffer. The buffer should include room for maxBufferCount bytes; this number should accomodate the expected size of the return value plus the NULL termination character, which this method adds. (So note that the maxLength passed to this method is one more than the one you would have passed to the deprecated getCString:maxLength:.) Use only with 8-bit encodings, and not encodings such as UTF-16 or UTF-32.

如果buffer太小，会导致转换出错

二 char* 转 NSString

1. initWithUTF8String:

NSString *string = [[NSString alloc] initWithUTF8String:cString];

2. initWithCString:encoding:

NSString *string = [[NSString alloc] initWithCString:cString encoding:NSUTF8StringEncoding];