在樹莓派零作業系統中編譯 ALSA 項目的 pcm.c 範例時出現問題
我正在使用帶有最新樹莓派作業系統的樹莓派零 W
我已經安裝了 libasound2 和 libasound2-dev，並且我從樹莓派論壇上下載的用於測試 alsa 庫的程式碼編譯並正確執行：
#include <stdio.h> #include <stdlib.h> #include <alsa/asoundlib.h> #include <alsa/pcm.h> int main() { int val; printf("ALSA library version: %s\n", SND_LIB_VERSION_STR); printf("\nPCM stream types:\n"); for (val = 0; val <= SND_PCM_STREAM_LAST; val++) printf(" %s\n", snd_pcm_stream_name((snd_pcm_stream_t)val)); return 0; }我正在嘗試在此處編譯 ALSA 項目網站中提供的正弦波生成範常式式碼：https ://www.alsa-project.org/alsa-doc/alsa-lib/_2test_2pcm_8c-example.html
這在他們的範例頁面中列為 pcm.c
我已將此程式碼保存在 main.cpp 中，並且我已更改
#include "../include/asoundlib.h"（這會導致編譯時找不到文件錯誤）為#include <alsa/asoundlib.h>我使用
gcc main.cpp -o main -lasound -fpermissive. 我收到一系列警告，但最後for (format = 0; format < SND_PCM_FORMAT_LAST; format++) {在它說有的行出現錯誤，no match for operator++並且operand type is 'snd_pcm_format_t' {aka '_snd_pcm_format'}). 但是根據他們的文件format已被聲明為static snd_pcm_format_t format = SND_PCM_FORMAT_S16;並且snd_pcm_format_t是一個列舉。我需要做什麼才能編譯這個基本範例？或者是否有一個更簡單的範例展示如何使用 C++ 在 ALSA 中生成正弦音，或者有一些部落格或教程解釋了 ALSA 的這個範常式式碼是如何工作的？
編輯：這些是在建構過程中看到的消息：[error is main.cpp:842:66: error: no match for ‘operator++’ ]
$ gcc main.cpp -o Main -lasound -fpermissive main.cpp:19:23: warning: ISO C++ forbids converting a string constant to ‘char*’ [-Wwrite-strings] static char *device = "plughw:0,0"; /* playback device */ ^~~~~~~~~~~~ main.cpp: In function ‘int write_and_poll_loop(snd_pcm_t*, short int*, snd_pcm_channel_area_t*)’: main.cpp:314:18: warning: invalid conversion from ‘void*’ to ‘pollfd*’ [-fpermissive] ufds = malloc(sizeof(struct pollfd) * count); ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ main.cpp: In function ‘void async_callback(snd_async_handler_t*)’: main.cpp:397:77: warning: invalid conversion from ‘void*’ to ‘async_private_data*’ [-fpermissive] ct async_private_data *data = snd_async_handler_get_callback_private(ahandler); ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~ main.cpp: In function ‘void async_direct_callback(snd_async_handler_t*)’: main.cpp:469:77: warning: invalid conversion from ‘void*’ to ‘async_private_data*’ [-fpermissive] ct async_private_data *data = snd_async_handler_get_callback_private(ahandler); ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~ main.cpp: In function ‘void help()’: main.cpp:756:53: warning: invalid conversion from ‘int’ to ‘snd_pcm_format_t’ {aka ‘_snd_pcm_format’} [-fpermissive] const char *s = snd_pcm_format_name(k); ^ In file included from /usr/include/alsa/asoundlib.h:54, from main.cpp:14: /usr/include/alsa/pcm.h:1065:56: note: initializing argument 1 of ‘const char* snd_pcm_format_name(snd_pcm_format_t)’ const char *snd_pcm_format_name(const snd_pcm_format_t format); ~~~~~~~~~~~~~~~~~~~~~~~^~~~~~ main.cpp: In function ‘int main(int, char**)’: main.cpp:842:27: warning: invalid conversion from ‘int’ to ‘snd_pcm_format_t’ {aka ‘_snd_pcm_format’} [-fpermissive] for (format = 0; format < SND_PCM_FORMAT_LAST; format++) { ^ main.cpp:842:66: warning: no ‘operator++(int)’ declared for postfix ‘++’, trying prefix operator instead [-fpermissive] for (format = 0; format < SND_PCM_FORMAT_LAST; format++) { ~~~~~~^~ main.cpp:842:66: error: no match for ‘operator++’ (operand type is ‘snd_pcm_format_t’ {aka ‘_snd_pcm_format’}) main.cpp:903:21: warning: invalid conversion from ‘void*’ to ‘short int*’ [-fpermissive] samples = malloc((period_size * channels * snd_pcm_format_physical_width(format)) / 8); ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ main.cpp:909:19: warning: invalid conversion from ‘void*’ to ‘snd_pcm_channel_area_t*’ {aka ‘_snd_pcm_channel_area*’} [-fpermissive] areas = calloc(channels, sizeof(snd_pcm_channel_area_t)); ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ $使用 g++ 而不是 gcc 會產生相同的錯誤
您正在嘗試將其編譯為 C++ 程序（“ISO C++ 禁止 …”）。因此，您會收到各種警告，因為包含的標頭是 C，而不是 C++。
重命名
main.cpp為main.c，以便將其編譯為 C 程序，或使用正確的 C++ 方式將 C 頭包含包裝到extern "C"中，然後使用g++，並確保您自己的程式碼符合 C++ 標準。