cocoa - NSString pointer passed to function... not keeping the value I set -

i'm not sure i'm doing wrong here. i've tried setting s1..3 in foo using:

s1 = [[nsstring alloc] initwithstring:[filepaths objectatindex:0]];

context below:

void foo(nsstring *s1, nsstring *s2, nsstring *s3){     //assign long string nsstring *fps     //...     //break fps smaller bits     nsarray *filepaths = [fps componentsseparatedbystring:@"\n"];     //the above worked! let's assign them pointers     s1 = [filepaths objectatindex:0];     //repeat s2 , s3     nslog(@"%@",s1); //it worked! we're done in function }  int main(int argc, const char * argv[]){     nsstring *s1 = nil; //s2 , s3     foo(s1,s2,s3); //this should work     nslog(@"%@",s1); //uh oh, null!     return 0; } 

no.

you passing in pointers objects can mutated locally. not changing original objects, might think plain c.

if want use method (which not recommend - it's odd see in cocoa except in case of nserror), have like:

void foo(nsstring **s1, nsstring **s2, nsstring **s3) {     *s1 = [filepaths objectatindex:0]; // etc. } 

you pass in &s1 argument.

this will, of course, clobber whatever in s1, potentially cause memory leaks, thread unsafety, etc., unless careful. why won't this.