Is there a way to specify argument position/index in NSString stringWithFormat?

Question

C# has syntax that allows you to specify the argument index in a string format specifier, e.g.:

string message = string.Format(\"Hello, {0}. You are {1} year         


        

Answer 1

The following code fixes the bug specified in this issue. It is a workaround and renumbers the placeholders to fill gaps.

+ (id)stringWithFormat:(NSString *)format arguments:(NSArray*) arguments 
{
    NSMutableArray *filteredArguments = [[NSMutableArray alloc] initWithCapacity:arguments.count];
    NSMutableString *correctedFormat = [[NSMutableString alloc ] initWithString:format];
    NSString *placeHolderFormat = @"%%%d$";

    int actualPlaceholderIndex = 1;

    for (int i = 1; i <= arguments.count; ++i) {
        NSString *placeHolder = [[NSString alloc] initWithFormat:placeHolderFormat, i];
        if ([format rangeOfString:placeHolder].location != NSNotFound) {
            [filteredArguments addObject:[arguments objectAtIndex:i - 1]];

            if (actualPlaceholderIndex != i) {
                NSString *replacementPlaceHolder = [[NSString alloc] initWithFormat:placeHolderFormat, actualPlaceholderIndex];
                [correctedFormat replaceAllOccurrencesOfString:placeHolder withString:replacementPlaceHolder];    
                [replacementPlaceHolder release];
            }
            actualPlaceholderIndex++;
        }
        [placeHolder release];
    }

    if (filteredArguments.count == 0) {
        //No numbered arguments found: just copy the original arguments. Mixing of unnumbered and numbered arguments is not supported.
        [filteredArguments setArray:arguments];
    }

    NSString* result;
    if (filteredArguments.count == 0) {
        //Still no arguments: don't use initWithFormat in this case because it will crash: just return the format string
        result = [NSString stringWithString:format];
    } else {
        char *argList = (char *)malloc(sizeof(NSString *) * [filteredArguments count]);
        [filteredArguments getObjects:(id *)argList];
        result = [[[NSString alloc] initWithFormat:correctedFormat arguments:argList] autorelease];
        free(argList);    
    }

    [filteredArguments release];
    [correctedFormat release];

    return result;
}