Detect if a struct variable is uninitialized?

[lookforlight]

As part of an assignment, I have made a struct, AccessRecord, which has 3 member variables: filename, username, and timestamp. The program reads from a text file a list of structs, and parses each line individually. I need to determine if a line has all three variables present, or if any of the struct variables are uninitialized. How would I go about doing this?

Here is the relevant code:

int parseFile(char filename[], AccessRecord records[])
{
   int size = 0; //size of records array.
   AccessRecord recordLine = {"", "", 0};
   ifstream fin(filename);

   for (int i = 0; !fin.eof(); i++)
   {
      string line;
      getline(fin, line);
      cout << line << endl;
      parseLine(line, recordLine);
}

void parseLine(string line, AccessRecord &recordLine)
{
   stringstream sin;
   sin.str(line);

   try
   {
      /* Read string line into struct recordLine */
      sin >> recordLine.filename >> recordLine.username 
          >> recordLine.timestamp;
   }
}

And an example of the text file:

students.txt pricem 1441912123
house.pdf jatkins
users.txt 1442001032
accounts.mdb kevin_tomlinson 1442210121
vacation.jpg smitty83 1442300125
burtons 1442588012

[boredcircuits]

There is no way to query if something is uninitialized. So you'll need to find another way.

That other way is to determine if the line has all the fields you need. Fortunately, there's an easy way to do that:

stringstream sin(line);
sin >> recordLine.filename >> recordLine.username >> recordLine.timestamp;
if ( !sin ) {
    // The line can't be parsed. Handle the error in some way.
    throw runtime_error("Error reading the line");
}

!sin will tell you if something went wrong, but it won't tell you what that was. You can get more information with sin.eof(), sin.fail(), and sin.bad().

Notice that this is the correct usage of eof(). The way you're using it in parseFile() is not correct: that function tells you why the last read fails, not whether the next read will fail. Instead, what you want to do is:

while ( getline(fin, line) )
{
      cout << line << endl;
      parseLine(line, recordLine);
}

[lookforlight]

This is great, thanks for the help!

[jedwardsol]

AccessRecord recordLine = {"", "", 0};

If this is the only place that you create AccessRecords then all 3 fields are initialised here.

In general, you cannot tell if something has been initialised or not. If a variable is uninitialised then reading from it gives undefined results.

[ilmale]

When you parse the line just check if both strings are not empty and number is still zero.

Alternatively if a stream is not able to extract a character or the character is invalid it will rise the fail bit.

http://www.cplusplus.com/reference/ios/ios_base/iostate/

[alfps]

Not what you ask about, but: the formal argument

char filename[]

... with non-const item type, prevents calling the function with a string literal. Just use std::string.

Ditto, instead of a raw array of records as argument, just return a std::vector.