What does this error mean: "error: expected specifier-qualifier-list before 'type_name'"?

I've been working on the Cell processor and I'm trying to create a struct that will hold an spe_context_ptr_t, which will be used within the thread to launch an spe context and will also hold a pointer to something else that will be passed to the spu context from within the thread (currently I'm trying to just make it a generic pointer, but in actuality it will be a pointer to another structure I've defined). When I try and compile, I get the following error:

spu/../common.h:38: error: expected specifier-qualifier-list before 'spe_context_ptr_t'

// here is the offending line(s)

typedef struct _PTHREAD_BLOCK {
    spe_context_ptr_t * context; // Error happens here
    uintptr32_t  args; 
 } PTHREAD_BLOCK;

The compiler doesn't know that spe_context_ptr_t is a type. Check that the appropriate typedef is in scope when this code is compiled. You may have forgotten to include the appropriate header file.

I had the same error message but the solution is different.

The compiler parses the file from top to bottom.

Make sure a struct is defined BEFORE using it into another:

typedef struct
{
	char name[50];
	wheel_t	wheels[4]; //wrong, wheel_t is not defined yet
} car_t;

typedef struct
{
	int weight;
} wheel_t;

For iPhone cocoa-touch projects:

I had this problem and thanks to Eric Farraro's comment, I was able to get it resolved. I was importing a class WSHelper.h in many of my other classes. But I also was importing some of those same classes in my WSHelper.h (circular like Eric said). So, to fix this I moved the imports from my WSHelper.h file to my WSHelper.m file as they weren't really needed in the .h file anyway.

You have to name your struct like that:

typedef struct car_t {

   char

   wheel_t

} car_t;

I got it with an import loop:

---FILE B.h
#import "A.h"
@interface B{
  A *a;
}
@end

---FILE A.h
#import "B.h"
@interface A{      
}
@end

I was able to sort this out using Gorgando's fix, but instead of moving imports away, I commented each out individually, built the app, then edited accordingly until I got rid of them.

this error basically comes when you use the object before using it.