The data member function in QByteArray can realize the mutual conversion between QByteArray and QString

char *QByteArray::data()

Returns a pointer to the data stored in the byte array. The pointer can be used to access and modify the bytes that compose the array. The data is '\0'-terminated, i.e. the number of bytes in the returned character string is size() + 1 for the '\0' terminator.

Example:

  QByteArray ba("Hello world");

  char *data = ba.data();

  while (*data) {

      cout << "[" << *data << "]" << endl;

      ++data;

  }

The pointer remains valid as long as the byte array isn't reallocated or destroyed. For read-only access, constData() is faster because it never causes a deep copy to occur.

This function is mostly useful to pass a byte array to a function that accepts a const char *.

The following example makes a copy of the char* returned by data(), but it will corrupt the heap and cause a crash because it does not allocate a byte for the '\0' at the end:

  QString tmp = "test";

  QByteArray text = tmp.toLocal8Bit();

  char *data = new char[text.size()]; // wrong here

  strcpy(data, text.data());

  delete [] data;

This one allocates the correct amount of space:

  QString tmp = "test";

  QByteArray text = tmp.toLocal8Bit();

  char *data = new char[text.size() + 1]; //correct

  strcpy(data, text.data());

  delete [] data;

Note: A QByteArray can store any byte values including '\0's, but most functions that take char * arguments assume that the data ends at the first '\0' they encounter.

See also constData() and operator[]().

-------------------------------------------------------------------------------------------------------------------------------

//Common parameter types: char * string, QByteArray character array, QString string

1. char* -------------> QByteArray               uses the constructor QByteArray(const char*)

char* str;
QByteArray byte(str);  //QByteArray constructor

2. char* -------------->QString                     uses the constructor QString(const char*)
char* str;
QString string(str);      //QString constructor

3、QByteArray   ------>char*                       使用成员函数 QByteArray::data()
QByteArray byte;
char* str = byte.data(); //QbyteArray::data()

4. QByteArray ------> QString                     uses the constructor QString(const QByteArray & ba )
QByteArray byte;
QString string(byte);  //QString constructor

5、QString  ----------> QByteArray             使用成员函数 QString::toAscii()
QString string;
QByteArray byte = string.toAscii();  //QString::toAscii

6、QString ------------>char*                       使用 qPrintable()
QString string;
char* str = qPrintable(string);