H:发出lws_write: C++字符串到C转换和发送
H:发出lws_write: C++字符串到C转换和发送
提问于 2019-10-23 04:22:00
我在用g++。
代码：
std::string str = "{\"action\":3,\"data\":{\"account\":\"somehashgoeshear\",\"someint\":0,\"id\":1,\"moreint\":0,\"name\":\"demo\"}}";
char *cstr = strdup(str.c_str());
lwsl_notice("\n%s", cstr);
return lws_write(wsi, (unsigned char*)cstr, strlen(cstr), LWS_WRITE_TEXT);这也不起作用：
std::string str = "{\"action\":3,\"data\":{\"account\":\"somehashgoeshear\",\"someint\":0,\"id\":1,\"moreint\":0,\"name\":\"demo\"}}";
return lws_write(wsi, (unsigned char*)str.c_str(), strlen(str.c_str()), LWS_WRITE_TEXT);但是，这很好(运行了很多次，没有什么错误)：
char cstr[96] = "{\"action\":3,\"data\":{\"account\":\"somehashgoeshear\",\"someint\":0,\"id\":1,\"moreint\":0,\"name\":\"demo\"}}";
return lws_write(wsi, (unsigned char*)cstr, strlen(cstr), LWS_WRITE_TEXT);还尝试用malloc创建字符串，但这也不起作用：
std::string str = "{\"action\":3,\"data\":{\"account\":\"somehashgoeshear\",\"someint\":0,\"id\":1,\"moreint\":0,\"name\":\"demo\"}}";
char *cstr = (char *)malloc((str.length() + 1) * sizeof(char));
strcpy(cstr, str.c_str());
lwsl_notice("\n%s", cstr);
return lws_write(wsi, (unsigned char*)cstr, strlen(cstr), LWS_WRITE_TEXT);我可以运行这段代码几次，但是最终我得到了这个错误：free(): invalid next size (fast) (在发送数据之后失败)
我也尝试过对LWS_PRE进行一些实验，但是当我将它添加到字符串中时，它在消息的开头添加了几个符号，比如：a":
当我在发送数据后尝试free(cstr)时，它会立即失败，并出现double free or corruption (out)错误。
lws版本:1.7.1os: ubuntu x64
回答 2
Stack Overflow用户
回答已采纳
发布于 2019-10-23 05:00:52
重要通知！
使用websocket协议发送时
LWS_WRITE_TEXT，LWS_WRITE_BINARY，LWS_WRITE_CONTINUATION，LWS_WRITE_PING，LWS_WRITE_PONG
或者在http/2上发送，
发送缓冲区必须在传递给lws_write()的缓冲区指针之前具有有效的lws_write字节。
这意味着您必须为缓冲区分配额外的LWS_PRE字节，即
std::string str(LWS_PRE, ' '); //Allocate LWS_PRE bytes
str += "{\"action\":3,\"data\":{\"account\":\"somehashgoeshear\",\"someint\":0,\"id\":1,\"moreint\":0,\"name\":\"demo\"}}"
return lws_write(wsi, (unsigned char*)&str[LWS_PRE], str.size(), LWS_WRITE_TEXT);使用malloc
char* createMessage() {
std::string str = "{\"action\":3,\"data\":{\"account\":\"somehashgoeshear\",\"someint\":0,\"id\":1,\"moreint\":0,\"name\":\"demo\"}}";
char *cstr = (char *)malloc(LWS_PRE + (str.length() + 1) * sizeof(char));
cstr += LWS_PRE;
strcpy(cstr, str.c_str());
lwsl_notice("\n%s", cstr);
return cstr;
}
...
char* msg = createMessage();
lws_write(wsi,
(unsigned char*)msg,
strlen(msg) /* add 1 if receiver expects the null character*/,
LWS_WRITE_TEXT);
free(msg - LWS_PRE);Stack Overflow用户
发布于 2022-03-23 12:47:39
使用libwebsocket发送C++字符串的简单方法：
std::string payload = "Some sample string.";
// prepare payload with lws header
std::string buffer(LWS_SEND_BUFFER_PRE_PADDING + payload.size(), ' ');
buffer.insert(LWS_SEND_BUFFER_PRE_PADDING, payload);
// send message
lws_write(wsi, (unsigned char*) &buffer[LWS_SEND_BUFFER_PRE_PADDING], payload.size(), LWS_WRITE_TEXT);页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/58515456
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