So I am using a parameterized type in a common module.
Is there a way to say:
if( type == TYPE1 ) assign the struct one way
else if( type == TYPE2 ) assign another way
I was picturing this in a generate block.
Yes, you can use the type operator do a generate-if/case, or procedural if/case like:
real r;
if ( type(r) == type(real) ) ...
But unfortunately the code in all branches still must successfully compile, regardless of the condition. You will not be able to reference struct member that does not exist.
typedef struct {int a;} s1_t;
typedef struct {int a;int b;} s2_t;
s1_t s;
initial
#1 // procedural-if
if (type(s) == type(s1_t))
$display("%m s.a = %0d",s.a);
else if (type(s) == type(s2_t))
$display("%m s.b ==%0d",s.b); // this will not compile
There is type() operator described in IEEE1800-2012 § 6.23. Example usage from from the LRM:
bit[12:0] A_bus, B_bus;
parameter typebus_t = type(A_bus);
generate
case(type(bus_t))
type(bit[12:0]): addfixed_int #(bus_t) (A_bus,B_bus);
type(real): add_float #(type(A_bus)) (A_bus,B_bus);
endcase
endgenerate
There is also $typename() described in IEEE1800-2012 § 20.6.1. $typename() return s string of the type. Example usage from from the LRM:
// source code // $typename would return
typedef bitnode; // "bit"
node [2:0] X; // "bit [2:0]"
int signedY; // "int"
packageA;
enum{A,B,C=99} X; // "enum{A=32'sd0,B=32'sd1,C=32'sd99}A::e$1"
typedef bit[9:1'b1] word; // "A::bit[9:1]"
endpackage: A
importA::*;
moduletop;
typedef struct{node A,B;} AB_t;
AB_t AB[10]; // "struct{bit A;bit B;}top.AB_t$[0:9]"
...
endmodule
Related
How i can use = operator overloading in a class in order to assign a value ??
int[4] users;
int someop(string op)(int j){
if(op == "="){
//example
users[j] = j
}
}
It is all in the documentation - https://dlang.org/spec/operatoroverloading.html#assignment ...
For details on how to overload other operators refer to the "Operator Overloading" section of the D Language Specification.
I'm passing an array of structs from Swift to a C function. The struct looks like this:
struct Struct {
int a;
float b;
float c;
const char* d;
const char* e;
const char* f;
const char* g;
int h[4];
};
Function signature of the C function:
void test(struct Struct* structs);
Weirdly, when I print d in the C function, it's often something different than what I set it to in the Swift code: usually an empty string or some garbage. When I set d to a very long string, it works correctly. The other strings are passed correctly too. Is that some struct alignment issue?
As #MartinR suggested, when I pass the string to the struct's constructor, Swift creates a temporary C char array on the stack, copies the string's data into it and passes its pointer to the constructor. Immediately after that, the char array is no longer valid. Here's an example code demonstrating this:
let s = Struct(string: "string")
print(s.string) // Prints "string"
print("lol") // Overwrite the stack
print(s.string) // Prints "lol"
See https://stackoverflow.com/a/40121697/243225 for possible solutions.
I have the following block code
typedef BOOL(^FieldValidationBlock)(NSString *);
FieldValidationBlock aBlock = ^(NSString *input){
return ([input length] == 10) ;
};
which throws me a compilation error thats tates the return type is int and should be BOOL.
when I add a cast it works just fine:
typedef BOOL(^FieldValidationBlock)(NSString *);
FieldValidationBlock aBlock = ^(NSString *input){
return (BOOL)([input length] == 10) ;
};
why this happen?
Because BOOL is an objective C type, and the logical comparison operators are standard C. In standard C the return type of comparison operators is an int. This is important to know sometimes, as when you negate a value that you assume to be boolean, but is in fact an int, it's not necessarily going to be what you expect.
In your example, casting to a BOOL is fine.
I'm having trouble creating this c struct in objective c.
typedef struct huffman_node_tag
{
unsigned char isLeaf;
unsigned long count;
struct huffman_node_tag *parent;
union
{
struct
{
struct huffman_node_tag *zero, *one;
};
unsigned char symbol;
};
} huffman_node;
I'm getting this warning at the end of the union type and the end of the struct type above the "unsigned char symbol variable"
warning: declaration does not declare anything
And then when i do something like this:
huffman_node *p = (huffman_node*)malloc(sizeof(huffman_node));
p->zero = zero;
I get this compilation error:
error: 'huffman_node' has no member named 'zero'
Why does this not work? Did i set this up incorrectly? Has anyone experienced this before?
typedef struct huffman_node_tag
{
unsigned char isLeaf;
unsigned long count;
struct huffman_node_tag *parent;
union
{
struct
{
struct huffman_node_tag *zero, *one;
}; // problematic here!
unsigned char symbol;
}; // another problem here!
} huffman_node;
Depending on the C dialect/compiler that is being used to interpret the code, you may not be allowed to declare a struct or union without a name. Try giving them names and see what happens. Alternatively, you may want to try and change the C dialect you are using.
As far as I know anonymous unions are not part of C, but are a compiler extension. So strictly your given struct definition is not valid C. Consequently it seems that objective C does not supports this extension.
You need to include the header for the C library you are using.
You shouldn't have to do much else than that, as Objective C, unlike C++, is a strict superset of C.
i got an error that said "error: conflicting types for '____'. What does that mean?
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.
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
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";
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.