25 BasicUsageEnvironment0基本使用环境基类——Live555源码阅读(三)UsageEnvironment

25 BasicUsageEnvironment0基本使用环境基类——Live555源码阅读(三)UsageEnvironment

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简介

BasicUsageEnvironment0

UsageEnvironment

纯虚接口

live555sourcecontrol\BasicUsageEnvironment\include\BasicUsageEnvironment0.hh

代码定义如下

// An abstract base class, useful for subclassing
// (e.g., to redefine the implementation of "operator<<")
class BasicUsageEnvironment0 : public UsageEnvironment {
public:
// redefined virtual functions:重定义虚函数

//返回fResultMsgBuffer
virtual MsgString getResultMsg() const;
// 调用reset将消息结果buffer截空，再将msg(msg1-3)拷贝到buffer
virtual void setResultMsg(MsgString msg);
virtual void setResultMsg(MsgString msg1,
MsgString msg2);
virtual void setResultMsg(MsgString msg1,
MsgString msg2,
MsgString msg3);
//将msg设置到fResultMsgBuffer，支持_WIN32_WCE的平台会将err代表的错误消息也加入
virtual void setResultErrMsg(MsgString msg, int err = 0);
//将msg拷贝到fResultMsgBuffer可用部分，剩余空间不够时，只拷贝部分
virtual void appendToResultMsg(MsgString msg);
////将fResultMsgBuffer中的内容写入到标准错误
virtual void reportBackgroundError();

protected:
BasicUsageEnvironment0(TaskScheduler& taskScheduler);
virtual ~BasicUsageEnvironment0();

private:
void reset();   //截空buffer字符串(首元素置'\0')

//消息处理结果缓冲
char fResultMsgBuffer[RESULT_MSG_BUFFER_MAX];
unsigned fCurBufferSize;    //当前buffer已用大小
unsigned fBufferMaxSize;    //最大buffer大小
};

BasicUsageEnvironment0构造析构与重置

UsageEnvironment

fBufferMaxSize

fResultMsgBuffer

#define RESULT_MSG_BUFFER_MAX 1000

reset

buffer

fResultMsgBuffer

BasicUsageEnvironment0::BasicUsageEnvironment0(TaskScheduler& taskScheduler)
: UsageEnvironment(taskScheduler),
fBufferMaxSize(RESULT_MSG_BUFFER_MAX) {
reset();
}

BasicUsageEnvironment0::~BasicUsageEnvironment0() {
}

void BasicUsageEnvironment0::reset() {
fCurBufferSize = 0;
fResultMsgBuffer[fCurBufferSize] = '\0';
}

ResultMsg系列方法

ResultMsg

一系列

fResultMsgBuffer

get/set/append/report

public权限

getResultMsg() const方法(获取buffer)

const

char const* BasicUsageEnvironment0::getResultMsg() const {
return fResultMsgBuffer;
}

appendToResultMsg方法(添加msg到buffer)

向buffer中添加内容

msg

char*

NULL

bug

strlen(NULL)

memmove(dest,NULL,len)

容不下msg

buffer

void BasicUsageEnvironment0::appendToResultMsg(MsgString msg) {
char* curPtr = &fResultMsgBuffer[fCurBufferSize];
unsigned spaceAvailable = fBufferMaxSize - fCurBufferSize;
unsigned msgLength = strlen(msg);

// Copy only enough of "msg" as will fit:
// fResultMsgBuffer剩余空间不够放，拷贝一部分
if (msgLength > spaceAvailable-1) {
msgLength = spaceAvailable-1;
}
/* memmove用于从src拷贝count个字符到dest，如果目标区域和源区域有重叠的话，memmove能够
保证源串在被覆盖之前将重叠区域的字节拷贝到目标区域中。但复制后src内容会被更改。但是当目标
区域与源区域没有重叠则和memcpy函数功能相同。*/
memmove(curPtr, (char*)msg, msgLength);
fCurBufferSize += msgLength;
fResultMsgBuffer[fCurBufferSize] = '\0';  //这个必须有
}

setResultMsg方法(重置buffer内容为msg)

重置buffer

C++的重载

参数不同

appendToResultMsg

// 调用reset将消息结果buffer截空，再将msg拷贝到buffer
void BasicUsageEnvironment0::setResultMsg(MsgString msg) {
reset();
appendToResultMsg(msg);
}

void BasicUsageEnvironment0::setResultMsg(MsgString msg1, MsgString msg2) {
setResultMsg(msg1);
appendToResultMsg(msg2);
}

void BasicUsageEnvironment0::setResultMsg(MsgString msg1, MsgString msg2,
MsgString msg3) {
setResultMsg(msg1, msg2);
appendToResultMsg(msg3);
}

setResultErrMsg方法(重置buffer内容为msg/err)

msg

buffer

err

windows(WIN32/WINCE)

getError()

BasicUsageEnvironment

return WSAGetLastError()

Windows Sockets API

errno

strerror(err)

buffer

void BasicUsageEnvironment0::setResultErrMsg(MsgString msg, int err) {
setResultMsg(msg);

#ifndef _WIN32_WCE
appendToResultMsg(strerror(err == 0 ? getErrno() : err));
#endif
}

reportBackgroundError方法(报告错误消息)

reportBackgroundError

buffer

stderr

无缓冲

//将fResultMsgBuffer中的内容写入到标准错误
void BasicUsageEnvironment0::reportBackgroundError() {
fputs(getResultMsg(), stderr);
}