Question

Hi
I use the following to convert std::string to NSString but it return (null) while trying to display the value of the nsstring

I need it to return instead of (null) empty at conversion time any suggestion

StudyDate=[NSString stringWithCString:studyDate length:strlen(studyDate)]; 

any suggestion to avoid null values

best regards

Answer 1

Edit: The syntax @"string" is used only for constructing NSString. With std::string you should use the standard "string" syntax.

NSString* aConstantNSString = @"foo";
const char* aConstantCString = "foo";
std::string aConstantStdString = "foo";
CFStringRef aConstantCFString = CFSTR("foo");

---

1. +stringWithCString:length: has been deprecated since the very early beginning of the iPhone SDK. If the string contains only ASCII characters, often you could use +stringWithUTF8String: instead.

2. Your method works only when studyDate is a C string (i.e. const char*), but you said you have a std::string. There is no method to directly convert a std::string into an NSString. You must use .c_str() to create the C string first:

   StudyDate = [NSString stringWithUTF8String:studyDate.c_str()];
   

   (But the above shouldn’t be the cause you’re getting (null) because passing a std::string to +stringWithCString:length: or even strlen should give a compile-time error immediately.

   'error: cannot convert ‘std::string’ to ‘const char*’ in argument passing'
   

   So studyDate should already be a const char*. We need more context (code) to see what’s going on.)