What does error conflicting types for '' mean? - iphone

Question

i got an error that said "error: conflicting types for '____'. What does that mean?

Answer 1

Quickfix:
Make sure that your functions are declared once and only once before they are called. For example, change:
main(){ myfun(3.4); }
double myfun(double x){ return x; }
To:
double myfun(double x){ return x; }
main(){ myfun(3.4); }
Or add a separate function declaration:
double myfun(double x);
main(){ myfun(3.4); }
double myfun(double x){ return x; }
Possible causes for the error
Function was called before being declared
Function defined overrides a function declared in an included header.
Function was defined twice in the same file
Declaration and definition don't match
Declaration conflict in the included headers
What's really going on
error: conflicting types for ‘foo’ means that a function was defined more than once with different type signatures.
A file that includes two functions with the same name but different return types would throw this error, for example:
int foo(){return 1;}
double foo(){return 1.0;}
Indeed, when compiled with GCC we get the following errors:
foo.c:5:8: error: conflicting types for ‘foo’
double foo(){return 1.0;}
^
foo.c:4:5: note: previous definition of ‘foo’ was here
int foo(){return 1;}
^
Now, if instead we had a file with two function definitions with the same name
double foo(){return 1;}
double foo(){return 1.0;}
We would get a 'redefinition' error instead:
foo.c:5:8: error: redefinition of ‘foo’
double foo(){return 1.0;}
^
foo.c:4:8: note: previous definition of ‘foo’ was here
double foo(){return 1;}
^
Implicit function declaration
So why does the following code throw error: conflicting types for ‘foo’?
main(){ foo(); }
double foo(){ return 1.0; }
The reason is implicit function declaration.
When the compiler first encounters foo() in the main function, it will assume a type signature for the function foo of int foo(). By default, implicit functions are assumed to return integers, and the input argument types are derived from what you're passing into the function (in this case, nothing).
Obviously, the compiler is wrong to make this assumption, but the specs for the C (and thus Objective-C) language are old, cranky, and not very clever. Maybe implicitly declaring functions saved some development time by reducing compiler complexity back in the day, but now we're stuck with a terrible feature that should have never made it into the language. In fact, implicit declarations were made illegal in C99.
That said, once you know what's going on, it should be easy to dig out the root cause of your problem.

Answer 2

it's probably because your function "_" already exists in your library. It happened to me with this function:
I was using stdio.h
int getline (char s[ ] , int lim)
{
int c, i;
for (i=0; i < lim-1 && (c=getchar())!=EOF && c!='\n'; ++i)
s[i] = c;
if (c == '\n') {
s[i] = c;
++i;
}
s[i] = '\0';
return i;
}
When I changed "getline" to "getlinexxx" and gcc compiled it:
int getlinexxx (char s[], int lim)
{
int c, i;
for (i=0; i < lim-1 && (c=getchar())!=EOF && c!='\n'; ++i)
s[i] = c;
if (c == '\n') {
s[i] = c;
++i;
}
s[i] = '\0';
return i;
}
And the problem was gone

Answer 3

What datatype is '___'?
My guess is that you're trying to initialize a variable of a type that can't accept the initial value. Like saying int i = "hello";

Answer 4

If you're trying to assign it from a call that returns an NSMutableDictionary, that's probably your trouble. Posting the line of code would definitely help diagnose warnings and errors in it.