gcc 错误：在“{”标记之前不允许使用函数定义

Question

不，我不知道出了什么问题。至少当我尝试将函数从 main 中取出并将其粘贴到 main 之前时，我收到的错误比以前更多。

我收到错误：

错误：在“{”标记之前不允许使用函数定义 void draw_spectrum(Display *display, Window window, double *magnitudes) {

使用此代码：

 
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <alsa/asoundlib.h>  // For audio capture
#include <X11/Xlib.h>       // For X11 graphics
#include "kiss_fft.h"       // For FFT calculations


int main(int argc, char*argv[]) {

/// Initialize audio capture and X11 display:

// Open audio device
snd_pcm_t *pcm_handle;
snd_pcm_open(&pcm_handle, "default", SND_PCM_STREAM_CAPTURE, 0);
// Set audio parameters (sample rate, channels, etc.)
snd_pcm_set_params(pcm_handle, SND_PCM_FORMAT_U8, SND_PCM_ACCESS_RW_INTERLEAVED, 1, 48000, 1, 500000);

// Open X11 display
Display *display = XOpenDisplay(NULL);
Window window = XCreateSimpleWindow(display, window, 100, 100, 800, 600, 1, BlackPixel(display, DefaultScreen(display)), WhitePixel(display, DefaultScreen(display))); //finish later...display, parent, x, y, width, height, border_width, border, background
XMapWindow(display, window);

/// Create buffers for audio samples and FFT output:

#define FFT_SIZE 1024  // Adjust as needed
kiss_fft_cfg cfg = kiss_fft_alloc(FFT_SIZE, 0, 0, 0);
kiss_fft_cpx in[FFT_SIZE];
kiss_fft_cpx out[FFT_SIZE];


    // Map magnitudes to visual representation (lines and bars)
void draw_spectrum(Display *display, Window window, double *magnitudes) {
  // Get window dimensions
  int width, height;
  XWindowAttributes wa;
  XGetWindowAttributes(display, window, &wa);
  width = wa.width;
  height = wa.height;

  // Calculate bar width and spacing
  int bar_width = width / (FFT_SIZE / 2 + 1);
  int bar_spacing = 1; // Adjust spacing as needed

  GC gc = XCreateGC(display, window, 0, NULL); // Create a graphics context

  // Clear the window (optional)
  XSetForeground(display, gc, WhitePixel(display, DefaultScreen(display)));
  XFillRectangle(display, window, gc, 0, 0, width, height);

  // Set drawing color for the bars
  XSetForeground(display, gc, BlackPixel(display, DefaultScreen(display)));

  // Draw bars for each magnitude value
  for (int i = 0; i < FFT_SIZE / 2 + 1; i++) {
    int bar_height = (int) (magnitudes[i] * height / 256); // Scale magnitude to screen height
    XFillRectangle(display, window, gc,
                   i * (bar_width + bar_spacing), height - bar_height,
                   bar_width, bar_height);
  }

  XFreeGC(display, gc); // Release the graphics context
}


    // Handle events and refresh display
    XNextEvent(display, ...);
    XFlush(display);
}


/// Main loop:

while (1) {
    // Capture audio samples
    snd_pcm_readi(pcm_handle, in, FFT_SIZE);

    // Apply window function (Hann window)
    for (int i = 0; i < FFT_SIZE; i++) {
        in[i].r *= 0.5 * (1 - cos(2 * M_PI * i / (FFT_SIZE - 1)));
    }

    // Perform FFT
    kiss_fft(cfg, in, out);

    // Calculate magnitudes
    double magnitudes[FFT_SIZE / 2 + 1];
    for (int i = 0; i < FFT_SIZE / 2 + 1; i++) {
        magnitudes[i] = sqrt(out[i].r * out[i].r + out[i].i * out[i].i);
    }

    // Map magnitudes to visual representation (lines and bars)
    draw_spectrum(display, window, magnitudes);

/// Clean up:

// Close audio device
snd_pcm_close(pcm_handle);

// Close X11 display
XDestroyWindow(display, window);
XCloseDisplay(display);

return 0;
}

我该如何解决这个问题？

Answer 1

标准 C 不允许将函数定义放在函数定义中（嵌套函数定义）。

在这种情况下，函数

main

没有引用函数

draw_spectrum

的局部变量，因此您可以通过将

draw_spectrum

的定义移到

main

之前来解决此问题。

此外，函数

}

中看起来有一个额外的

draw_spectrum

，而主循环周围缺少

}

。您应该对代码应用适当的缩进，以便更容易找到此类错误。

另一点是，在函数调用中使用

...

（如

XNextEvent(display, ...);

）看起来无效。你应该用合适的东西替换它。