CODEWITHSUNDEEP
objective-cnsstringvariadic-functions
jowie
jowie

Reputation: 8068

Variadic function: Checking number of arguments

I have a variadic function that runs some code on the first argument and then runs NSString initWithFormat:arguments: afterwards, if arguments have been passed in.

+ (NSString *)updatedString:(NSString *)mainString, ...
{
    // Some code run on mainString here, outputs finalString

    // add format arguments to the final string
    va_list args;
    va_start(args, mainString);
    NSString *formattedString = [[NSString alloc] initWithFormat:finalString arguments:args];
    va_end(args);

    return formattedString;
}

EDIT: The idea is that the code run on mainString uses a regular expression to find and replace variables within the text. So say the output (finalString) equals "Hello World %@ blah blah %@", then it would use the arguments to replace the %@ symbols. The issue is that I don't know if the resolved string includes %@ symbols or not until the string is resolved.

So, I need to check to see if there are actually any extra arguments, and if there aren't, I don't want to run the initiWithFormat part.

Is there any way to check if args exists first?

Upvotes: 0

Views: 221

Answers (1)

newacct
newacct

Reputation: 122439

No. In C/Objective-C a called variadic function has absolutely no idea about the number and types of arguments passed by the caller. It must figure it out somehow based on other information (e.g. for format arguments, that they match the format specifiers in the format string; or for objects to initialize a Cocoa collection, that the list is terminated with nil) and trust that the caller correctly followed the convention.

Upvotes: 3

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