CODEWITHSUNDEEP
c++objective-cxamarin.iosobjective-c++
BruceHill
BruceHill

Reputation: 7164

Converting a C++ GUID structure to NSString* in Objective-C++

I am trying to implement the following method in Objective-C:

- (NSString*) getGuidWithCid: (int) cid;

This method must retrieve a GUID from a database using a C++ API and then convert this GUID into a string representation of the GUID. The structure GUID returned by the C++ API has the following definition:

typedef struct _GUID {
    ul_u_long   Data1;
    ul_u_short  Data2;
    ul_u_short  Data3;
    ul_byte     Data4[ 8 ];
} GUID;

Here is my attempt to implement this method:

- (NSString*) getGuidWithCid: (int) cid
{
    GUID ulguid;
    ((ULResultSet *) ulresultset)->GetGuid([cname UTF8String], &ulguid);
    NSString* data4 = [[[NSString alloc] initWithBytes:ulguid.Data4
                                         length:8
                                         encoding: NSUTF8StringEncoding] autorelease];
    return [NSString stringWithFormat:@"%u-%uh-%uh-%@", 
                     ulguid.Data1, 
                     ulguid.Data2,
                     ulguid.Data3, 
                     data4];
}

The first two lines of this method are working fine, so the variable ulguid contains a valid guid. The problem I am having is with the conversion of the byte array portion of the GUID (ie. Data4 in the GUID structure). What I am getting back from this method currently is three numeric values separated by hyphens, so Data1, Data2 and Data3 seem to be represented correctly, but NULL is being shown for Data4. What am I doing wrong here?

Upvotes: 1

Views: 914

Answers (3)

BruceHill
BruceHill

Reputation: 7164

I have successfully implemented this method as follows:

- (NSString*) getGuidWithCid: (int) cid
{
    GUID ulguid;
    ((ULResultSet *) ulresultset)->GetGuid(cid, &ulguid);

    char buffer[37];

    sprintf(buffer, "%08X-%04X-%04X-%02X%02X-%02X%02X%02X%02X%02X%02X",
                    ulguid.Data1, ulguid.Data2, ulguid.Data3,
                    ulguid.Data4[0], ulguid.Data4[1],
                    ulguid.Data4[2], ulguid.Data4[3],
                    ulguid.Data4[4], ulguid.Data4[5],
                    ulguid.Data4[6], ulguid.Data4[7]);

    return [[[NSString alloc] initWithBytes:buffer 
                              length:sizeof(buffer) 
                              encoding:NSASCIIStringEncoding] autorelease];
}

Thanks goes to Ferdinand Beyer (http://stackoverflow.com/users/34855/ferdinand-beyer) for helping me get to this solution.

Upvotes: 1

fbrereto
fbrereto

Reputation: 35925

You are calling release on data4 immedaitely after you create it. The contents of the string, therefore, are invalid at the point you try to use it. Consider calling autorelease instead.

Upvotes: 4

Caleb
Caleb

Reputation: 124997

It's possible that the bytes in ulguid.Data4 don't form a valid UTF8 string, so you get nil back when you try to create a string with those bytes.

Upvotes: 2

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