Pass and access structures using objective-c

Question

I want to know how to pass structures to another function and subsequently access that structure in the called function. I'm developing for the iPhone and the reason I'm using structs is so that I can eventually pass data as structs to a server being built in C.

Here's the structure:

struct userInfo{
    NSString *firstName;
    NSString *lastName;
    NSString *username;
    NSString *email;
    NSString *ipAddress;
    double latitude;
    double longitude;
};

Here I'm simply fetching some user inputed data along with some CoreLocation data and the iPhone's IP Address:

- (IBAction)joinButton {
    struct userInfo localUser;

    localUser.firstName = firstName.text;
    localUser.lastName = lastName.text;
    localUser.username = username.text;
    localUser.email = emailAddress.text;
    localUser.ipAddress = localIPAddress.text;
    localUser.latitude = currentLocation.coordinate.latitude;
    localUser.longitude = currentLocation.coordinate.longitude;

    [myNetworkConnection registerWithServer:&localUser];
}

function handling the struct:

- (void)registerWithServer:(struct userInfo*)myUser {

    printf("First name is: %s", myUser.firstName);//error when compiling
}

the complier throws this error: request for member 'firstName' in something not a structure or union. Is that struct out of scope when I try to access it in the second function?

There's no reason to put Objective-C objects inside of structs. Don't do it. Either make an object to hold your data, put it in an NSDictionary, or convert everything to native C types like char* for your struct. — Jim Puls
– Jim Puls, Commented Jun 30, 2009 at 17:01

Matt K · Accepted Answer · 2009-06-30 15:54:50Z

7

You are passing in a pointer to a struct. Use the -> operator, not the dot.

myUser->firstName

answered Jun 30, 2009 at 15:54

Matt K

14k3 gold badges36 silver badges54 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

Eric de Araujo Over a year ago

that outputs 8a on the console, which isn't the inputed string.

Matt K Over a year ago

That's because it's an NSString, not a C string (char *). You can get a C string with a copy of the NSString's contents using the cStringUsingEncoding:, getCString:maxLength:encoding:, or UTF8String methods. The last may be the easiest: printf("%s\n", [myUser->firstName UTF8String]);

Quinn Taylor Over a year ago

To output an NSString with printf(), you have to convert it to a char* and use the %s format specifier. However, you can use %@ with NSLog, or with your own variant. cocoaheads.byu.edu/wiki/a-different-nslog

Eric de Araujo Over a year ago

Thanks. I should figured that one out. Since these structs are eventually going to get passed to the server I'm now thinking I should define the struct using char arrays instead of NSStrings.

Matt K Over a year ago

In this case, you probably want to make sure the structs are aligned to the same width on both client and server.

|

Kendall Helmstetter Gelner · Accepted Answer · 2009-06-30 16:54:53Z

2

I can't help but think you should really make that a proper objective-C object with properties - more work but then it'll all behave better and live within the NSObject ecosystem.

answered Jun 30, 2009 at 16:54

Kendall Helmstetter Gelner

75.1k27 gold badges132 silver badges151 bronze badges

2 Comments

Eric de Araujo Over a year ago

right, and it will probably get to that. but right now I want to get comfortable sending a struct from the iPhone to a remote server. I imagine that in the future this will be an object and i'll copy it's properties in a struct to push out.

Kendall Helmstetter Gelner Over a year ago

Instead of writing a custom C server that pulls apart a binary structure built on an entirely different architecture from the server code, instead consider building out a simple REST style web service where you pass up new data as parameters instead... this will make life far, far easier for you in the long run. Otherwise start reading up on endian issues and how to adapt for differing int sizes in structures...

Collectives™ on Stack Overflow

Pass and access structures using objective-c

2 Answers 2

6 Comments

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

6 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related