Sscanf Equivalent in Objective-C

Question

I'm currently writing a wavefront OBJ loader in Objective-C and I'm trying to figure out how to parse data from an NSString in a similar manner to the sscanf() function in C.

OBJ files define faces in x,y,z triplets of vertices, texture coordinates, and normals such as:

f 1.43//2.43 1.11//2.33 3.14//0.009

I'm not concerned about texture coordinates at the current moment. In C, an easy way to parse this line would be a statement such as:

sscanf(buf, "f %d//%d %d//%d %d//%d", &temp[0], &temp[1], &temp[2], &temp[3], &temp[4], &temp[5]);

Obviously, NSStrings can't be used in a sscanf() without first converting them to a C-style string, but I'm wondering if there's a more elegant way to performing this without doing such a conversion.

Answer 1

The NSScanner class can parse numbers in strings, although it can't be used as a drop-in replacement for sscanf.

Edit: here's one way to use it. You can also put the / into the list of characters to be skipped.

float temp[6];
NSString *objContent = @"f 1.43//2.43 1.11//2.33 3.14//0.009";
NSScanner *objScanner = [NSScanner scannerWithString:objContent];

// Skip the first character.
[objScanner scanString:@"f " intoString:nil];

// Read the numbers.
NSInteger index=0;
BOOL parsed=YES;
while ((index<6)&&(parsed))
{
    parsed=[objScanner scanFloat:&temp[index]];
    // Skip the slashes.
    [objScanner scanString:@"//" intoString:nil];

    NSLog(@"Parsed %f", temp[index]);
    index++;
}

Answer 2

To go from an NSString to an C-String (char *), use

NSString *str = @"string";
const char *c = [str UTF8String];

Alternatively,

NSString *str = @"Some string";
const char *c = [str cStringUsingEncoding:NSUTF8StringEncoding];

Provide access to the sscanf() function.

To go the other way, use

const *char cString = "cStr";
NSString *string = [NSString stringWithUTF8String:cString];

Or

const *char cString = "cStr";
NSString *myNSString = [NSString stringWithCString:cString encoding:NSASCIIStringEncoding];

From a pure ObjC standpoint, NSScanner provides the -scanInteger or -scanFloat methods to pull ints and floats out of a string.

NSScanner *aScanner = [NSScanner scannerWithString:string];
[aScanner scanInteger:anInteger];