被调用的对象不是函数或函数指针

Question

我正在编写一个低通滤波器的程序。当我编译时，出现以下错误:

called object is not a function or function pointer

对于我用 double 声明的变量。知道为什么会发生这种情况吗？

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int main(int argc, char **argv) {
  double omega1, omega2, omegac, T, dt;
  int N, method;
  FILE *in;

  // Open the file and scan the input variables.
  if (argv[1] == NULL) {
    printf("You need an input file.\n");
    return -1;
  }
  in = fopen(argv[1], "r");
  if (in == NULL)
    return -1;
  fscanf(in, "%lf", &omega1);
  fscanf(in, "%lf", &omega2);
  fscanf(in, "%lf", &omegac);
  fscanf(in, "%d", &method);

  T = 3 * 2 * M_PI / omega1; // Total time
  N = 20 * T / (2 * M_PI / omega2); // Total number of time steps
  dt = T / N;   // Time step ("delta t")

  // Method number 1 corresponds to the finite difference method.
  if (method == 1) {
    int i;
    double Voutnew = 0, Voutcur = 0, Voutprev = 0;

    for (i = N; i != 0; i--) {
      Voutnew = ((1/((1/((sqrt(2))(dt)(omegac))) + (1/((dt)(dt)(omegac) (omegac))))) * (((2/((dt)(dt)(omegac)(omegac))) - 1)(Voutcur) + (1/((1/((sqrt(2))(dt)(omegac))) - (1/((dt)(dt)(omegac)(omegac)))))(Voutprev) + Sin((omega1)(T)) + (1/2)(Sin((omega2)(T)))));
      Voutcur = Voutnew; // updates variable
      Voutprev = Voutcur;   // passes down variable to next state
      printf("%lf\n", Voutnew);
    }
  } else {
    // Print error message.
    printf("Incorrect method number.\n");
    return -1;
  }
  fclose(in);
  return 0;
}

这是我收到的错误列表:

In function 'main':
Line 38: error: called object '1.41421356237309514547462185873882845044136047363e+0' is not a function
Line 38: error: called object 'dt' is not a function
Line 38: error: called object 'dt' is not a function
Line 38: error: called object '1.41421356237309514547462185873882845044136047363e+0' is not a function
Line 38: error: called object 'dt' is not a function
Line 38: error: called object 'omega1' is not a function
Line 38: error: called object 'omega2' is not a function
Line 38: error: called object '0' is not a function

Answer 1

您需要乘法运算符

((sqrt(2))(dt)(omegac)

例如，这是错误的，您应该在我至少知道的所有编程语言中显式指定乘法运算符

sqrt(2) * dt * omegac

此外，使用太多括号会使代码很难阅读，所以不要这样做。

使用括号是错误消息的情况，因为

(dt)(omegac)

被解释为好像 dt 是一个函数，而 omegac 是传递给它的参数，并且由于 dt 不是函数，因此错误消息是有道理的。

这只是需要修复的代码的一小部分，如果我是你，我会将表达式拆分为子表达式，在你的大错误中并不容易看到错误。

对 Sin 的 undefined reference 是因为 c 区分大小写，没有名为 Sin 的函数，它是 sin。