I have a structure that stores coordinates (x_i,y_i).

typedef struct _FCOORD{
    float X;
    float Y;
}FCOORD,*PFCOORD;

Now I define a variable named point and store some data

FCOORD point;
point.X=20.00f;
point.Y=20.00f;

I want to just load data like this:

point={20.00f,20.00f};

I am coding in C language using gcc compiler

C:\My_Assets\MinGW\bin>gcc --version
gcc (x86_64-posix-seh-rev0, Built by MinGW-W64 project) 7.3.0
Copyright (C) 2017 Free Software Foundation, Inc.

I get this error when compiling

gcc -c ./src/main.c -I"F:\Codes\Windows\Application\include"
In file included from ./src/main.c:13:0:
./src/threads.c: In function 'WorkerThread':
./src/threads.c:66:19: error: expected expression before '{' token
     R1_data.start={10,10};
                   ^

EDIT: Please mention similar case for structure pointer too i.e PFCOORD. Thank you.

CodePudding user response：

You can use a compound literal for such an assignment:

#include <stdio.h>

typedef struct FCOORD {
    float X;
    float Y;
} FCOORD;

int main()
{
    FCOORD point;
    point.X = 20.00f;
    point.Y = 20.00f;

    point = (FCOORD){ 42.00f, 3.1415927f }; // The RHS here is a compound literal

    printf("%f %f\n", point.X, point.Y);
    return 0;
}

Note that, as mentioned on the linked cppreference page, although they look a lot like casts, compound literals are not casts and behave very differently.

Also note that I removed the leading underscore from your _FCOORD type name; identifiers with leading underscores followed by an uppercase letter are reserved for use by the implementation.

You can also add designated initializers to the assignment shown in the code above; this may be useful if you want to assign the elements "out of order", or if there are other structure members that you don't want to explicitly assign¹. Using these, the line would be like this:

    point = (FCOORD){ .Y = 3.1415927f, .X = 42.00f };

¹ But, be careful in the latter case (where you have members that are not explicitly set in the compound literal): These will not keep their 'original' values but will, instead, be default initialized.

CodePudding user response：

You can do this when declaring and initializing at the same time.

typedef struct A { int b; int c; } At;

int main(void) {
  At a = {.b=42, .c=27};

  return 0;
}

But you cannot use this after declaration. This will not compile.

typedef struct A { int b; int c; } At;

int main(void) {
  At a;
  a = {.b=42, .c=27};

  return 0;
}

Outside of initialization, you can assign a compound literal. Note that this is a C99 feature, and you may have problems with this if using an older compiler. If so, get a new compiler.

typedef struct A { int b; int c; } At;

int main(void) {
  At a;
  a = (At){.b=42, .c=27};

  return 0;
}