[英]How to redirect stdout to stderr
I am working with a C++ QT application that also uses JavaScript.我正在使用 C++ QT 应用程序,该应用程序也使用 JavaScript。 In C++ I use the qDebug function and capture all data with qInstallMessageHandler.在 C++ 中,我使用 qDebug function 并使用 qInstallMessageHandler 捕获所有数据。
This captures everything that is directed to stderr.这会捕获指向 stderr 的所有内容。 In JavaScript I am using console.info which writes data to stdout.在 JavaScript 中,我使用 console.info 将数据写入标准输出。
What I want to do is redirect stdout to stderr so that all the messages written by console.info find they're way into the same message handler.我想要做的是将stdout重定向到stderr,以便console.info写入的所有消息都找到它们进入同一个消息处理程序的方式。
void qDebugMsgHandler(QtMsgType type, const QMessageLogContext& context, const QString& strMsg) {
QString strOutput;
if ( context.file ) {
strOutput += QString(context.file);
if ( context.function ) {
if ( context.line > 0 ) {
strOutput += QString(" L%1").arg(context.line, 8, 10, QChar('0')) + QString(":");
}
strOutput += QString(context.function);
}
}
if ( strMsg.length() > 0 ) {
if ( strOutput.length() > 0 ) {
strOutput += ": ";
}
strOutput += strMsg;
}
switch( type ) {
case QtDebugMsg:
fprintf(stderr, " Debug:%s\n", strOutput.toLatin1().data());
break;
case QtInfoMsg:
fprintf(stderr, " Info:%s\n", strOutput.toLatin1().data());
break;
case QtWarningMsg:
fprintf(stderr, " Warning:%s\n", strOutput.toLatin1().data());
break;
case QtCriticalMsg:
fprintf(stderr, "Critical:%s\n", strOutput.toLatin1().data());
break;
case QtFatalMsg:
fprintf(stderr, " Fatal:%s\n", strOutput.toLatin1().data());
break;
}
fflush(stderr);
}
You can use ios::rdbuf .您可以使用ios::rdbuf 。
Example:例子:
#include <iostream>
int main() {
std::cout << "to stdout\n";
std::cout.rdbuf(std::cerr.rdbuf());
std::cout << "to stderr\n";
}
For my purpose, I ended up created an invokable routine in C++ which could be called from the JavaScript, C++ prototype:出于我的目的,我最终在 C++ 中创建了一个可调用例程,该例程可以从 JavaScript、C++ 原型中调用:
Q_INVOKABLE void log(QString strMsg, QString strFile, long ulngLine);
C++ implementation: C++ 实现:
void clsScriptHelper::log(QString strMsg, QString strFile, long ulngLine) {
QJsonObject json;
json["file"] = strFile;
json["line"] = QString("%1").arg(ulngLine);
json["msg"] = strMsg;
json["type"] = QString("%1").arg(QtDebugMsg);
qDebug() << json;
}
In the JavaScript I expose my C++ layer through the object reference "api", then call the log routine:在 JavaScript 我通过 object 引用“api”公开我的 C++ 层,然后调用日志例程:
api.log("Testing", "SomeFile.js", 99);
The message handler now looks like this:消息处理程序现在看起来像这样:
void qDebugMsgHandler(QtMsgType type, const QMessageLogContext& context, const QString& strMsg) {
static const QString scstrQJSONObject("QJsonObject(");
QString strFile, strFunction, strInfo, strOutput;
long lngLine = 0;
switch( type ) {
case QtDebugMsg:
strOutput = " Debug:";
break;
case QtInfoMsg:
strOutput = " Info:";
break;
case QtWarningMsg:
strOutput = " Warning:";
break;
case QtCriticalMsg:
strOutput = "Critical:";
break;
case QtFatalMsg:
strOutput = " Fatal:";
break;
}
if ( strMsg.startsWith(scstrQJSONObject) ) {
//Message contains a JSON object, extract the details
int intLength = strMsg.length() - (scstrQJSONObject.length() + 1);
QString strJSON = strMsg.mid(scstrQJSONObject.length(), intLength);
QJsonDocument objDoc = QJsonDocument::fromJson(strJSON.toUtf8());
if ( objDoc.isNull() ) {
return;
}
QJsonObject objJSON = objDoc.object();
strFile = objJSON.take("file").toString();
lngLine = static_cast<long>(objJSON.take("line").toDouble());
strInfo = objJSON.take("msg").toString();
type = static_cast<QtMsgType>(objJSON.take("type").toInt());
} else {
strFile = QString(context.file);
if ( context.function ) {
strFunction = QString(context.function);
}
if ( context.line > 0 ) {
lngLine = context.line;
}
strInfo = strMsg;
}
if ( strFile.length() > 0 ) {
strOutput += strFile;
}
if ( lngLine > 0 ) {
strOutput += QString(" L%1").arg(lngLine, 8, 10, QChar('0')) + QString(":");
}
if ( strFunction.length() > 0 ) {
strOutput += strFunction;
}
if ( strInfo.length() > 0 ) {
if ( strOutput.length() > 0 ) {
strOutput += ": ";
}
strOutput += strInfo;
}
std::cout << strOutput.toLatin1().data() << std::endl << std::flush;
}
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