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I wanted to get gpu name, and found the code that does this using IOKit. The only problem is that this code was in Objective-C, while my project is in C, and I don't know how to use C-string instead of NSString.

const void *GPUModel = CFDictionaryGetValue(serviceDictionary, CFSTR("model"));

            if (GPUModel != NULL) {
                if (CFGetTypeID(GPUModel) == CFDataGetTypeID()) {
                    //(Original Comment) Create a string from the CFDataRef.
                    //NSString *modelName = [[NSString alloc] initWithData:
                    //                       (NSData *)GPUModel encoding:NSASCIIStringEncoding];

                }
            }
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  • 2
    Looks like GPUModel is CFDataRef. There is all C functions you need developer.apple.com/documentation/corefoundation/… Commented Aug 30, 2021 at 15:45
  • 1
    The specific routine you want is CFDataGetBytePtr. Note that it likely won't be NULL-terminated, so you'll probably need to copy the values into another buffer to add the NULL. Commented Aug 30, 2021 at 15:54
  • Thanks guys, you really rock. As I tested it is Null terminated, but I will check it one more time. Commented Aug 30, 2021 at 16:00
  • Yeah, recieved string lenght is 28. Commented Aug 30, 2021 at 16:13
  • 2
    The code you posted is C, not Objective-C. The question is how do I convert a CFDataRef to a C string. Commented Aug 31, 2021 at 5:09

2 Answers 2

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C-like strings are actually char pointers aka char array, that stores each character. In the case of Obj-c NSString is a class that has a char array inside, and those methods that are used to modify your string value are just methods, and NSString itself uses C-style strings such as char array. So if you want to work with a C-style string you Have to use char arrays that is compatible with Obj-C because it is just a primitive data type.

If you will need further assistance, feel free to reply. Best, regards.

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Yes I know that C-strings are char pointers to array and this is not about converting NSString to C-String. I need to covert this: NSString *modelName = [[NSString alloc] initWithData: (NSData *)GPUModel encoding:NSASCIIStringEncodi to C code (without Foundation as it doesn't work with C). The problem is, you cannot just change NSString to char * and assign it to GPUModel void pointer, as this won't work.
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Solution thanks to Cy-4AH and Rob Napier.

const char *gpu_name = (char *)CFDataGetBytePtr(GPUModel);
return gpu_name;
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3 Comments

You need turn on malloc scribble in xcode run options, to be sure, that you have null-terminated string. There is exist possibility that you just have tested on clear memory segment
I don't use xcode, so i'll just have to check it by ascii values.
Then you need to find how to turn on the same behaviour in yours environment

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