script/expr_w_vars

• C

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  #include <expr_w_vars.h>
  #include <stdio.h>
   
  // This example shows how to run an expression that uses variables. Variables
  // make it possible to change the inputs to an expression after the expression
  // has been parsed. This example also shows how to parse an expression and 
  // evaluate it multiple times.
   
  int main(int argc, char *argv[]) {
      ecs_world_t *world = ecs_init_w_args(argc, argv);
   
      // Declare variables that we'll use in the expression
      ecs_script_vars_t *vars = ecs_script_vars_init(world);
      ecs_script_var_t *x = ecs_script_vars_define(vars, "x", ecs_i32_t);
      ecs_script_var_t *y = ecs_script_vars_define(vars, "y", ecs_i32_t);
   
      // Assign values to variables
      *(int32_t*)x->value.ptr = 10;
      *(int32_t*)y->value.ptr = 20;
   
      // Declare value that will hold the expression result. Specify that we want
      // the returned value to be of type i32. If the expression type doesn't 
      // match the specified type, it will be casted.
      int32_t result = 0;
      ecs_value_t result_value = {
          .type = ecs_id(ecs_i32_t),
          .ptr = &result
      };
   
      // Parse expression
      ecs_expr_eval_desc_t desc = { .vars = vars };
      ecs_script_t *s = ecs_expr_parse(world, "$x + $y", &desc);
      if (!s) {
          printf("failed to parse expression\n");
          return -1;
      }
   
      // Evaluate expression with variables
      if (ecs_expr_eval(s, &result_value, &desc)) {
          printf("failed to evaluate expression\n");
          return -1;
      }
   
      printf("result = %d\n", result);
   
      // Change variable and reevaluate expression
      *(int32_t*)y->value.ptr = 30;
      if (ecs_expr_eval(s, &result_value, &desc)) {
          printf("failed to evaluate expression\n");
          return -1;
      }
   
      printf("result = %d\n", result);
   
      // Free resources
      ecs_script_vars_fini(vars);
      ecs_script_free(s);
   
      return ecs_fini(world);
   
      // Output
      //  result = 30
      //  result = 40
  }