我很难在Qt中通过struct
向QFile
写一个文件。
typedef struct {
uint32_t timestamp;
uint32_t recordType;
uint32_t payloadLength;
char* payload;
} DataPacket;
DataPacket
结构填充在别处:
QString dataString = "$GPGSA,M,3,03,23,22,19,17,01,09,31,12,,,,1.9,0.9,1.6*3D";
DataPacket p;
memset(&p, 0, sizeof(DataPacket));
p.timestamp = now();
p.recordType = 1;
QByteArray arr = dataString.toLatin1();
p.payloadLength = arr.count();
p.payload = arr.data();
// Write the data to a log file
QFile f;
f.setFileName(outputFile);
bool ok = f.open(QIODevice::WriteOnly);
if (ok) {
f.write((char *)&p, sizeof(DataPacket));
f.close();
}
当我检查outputFile
日志文件时,$GPGSA...
字符串无处可见。如果我再单独写payload
字段:
if (ok) {
f.write((char *)&p, sizeof(DataPacket));
f.write(p.payload, p.payloadLength);
f.close();
}
随后正确写入$GPGSA
字符串。
我错过了什么......
答案 0 :(得分:1)
另一件事是保持Qt兼容性重命名一些本机类型,所以我建议使用等效类型,除了直接使用QString而不是char * payload和payloadLength,如下所示:
struct DataPacket{
quint32 timestamp;
quint32 recordType;
QString payload;
};
另外,写作时最好使用QDataStream
,如下所示:
QDataStream &operator>>(QDataStream &in, DataPacket &p){
in >> p.timestamp >> p.recordType >>p.payload;
return in;
}
QDataStream &operator<<(QDataStream &out, const DataPacket &p){
out << p.timestamp << p.recordType <<p.payload;
return out;
}
以下示例显示了它的用法:
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
const QString fileName = "file.log";
QString dataString = "$GPGSA,M,3,03,23,22,19,17,01,09,31,12,,,,1.9,0.9,1.6*3D";
DataPacket pin{1000, 123, dataString};
QFile fout(fileName);
if(fout.open(QIODevice::WriteOnly)){
QDataStream out(&fout);
out<<pin;
}
fout.flush(); // or fout.close();
DataPacket pout;
QFile fin(fileName);
if (fin.open(QIODevice::ReadOnly)) {
QDataStream in(&fin);
in>>pout;
qDebug()<<pout.timestamp<<pout.recordType<<pout.payload;
}
return 0;
}
输出:
1000 123 "$GPGSA,M,3,03,23,22,19,17,01,09,31,12,,,,1.9,0.9,1.6*3D"
注意: QDataStream间接设置payloadLength,因为它知道QString的大小。
答案 1 :(得分:0)
简单得多:
假设您的结构为“ DataPacket”
void MyClass::write()
{
QFile out(FILE_PATH_NAME);
out.open(QIODevice::WriteOnly);
out.write((const char *)DataPacket,sizeof(DataPacket));
out.close();
}
void MyClass::read()
{
QFile in(FILE_PATH_NAME);
in.open(QIODevice::ReadOnly);
in.read((const char *)DataPacket,sizeof(DataPacket));
in.close();
}