ifstream loop to only read when "=" is found [closed] - c++

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I'm fairly new to C++. I'm creating a program that uses multiple .dat input files. In these input files <double>, <int>, <char> and <bool> variable definitions are stored. Variables are declared within the program itself. I want the input files to be somewhat user friendly, therefore I added text to clarify.
I'm using ifstream with overload parameter >> to read the input files. To ignore redundant text I'm using .ignore(256, '\n') and to find a variable definition .ignore(256, '=').
The code I'm using works, but it looks ridiculous. How can I improve this code to just read all the lines with a = symbol?
Below a representation of what I'm doing right now. I chose .dat for input because I'm using .txt for output. It just makes the files a bit more recognizable, but I don't mind changing to .txt if necessary.
inputfile.dat
IGNORE THIS LINE
IGNORE THIS LINE
IGNORE THIS LINE
IGNORE THIS LINE
IGNORE THIS LINE
var1 = 1 2 3
var2 = 4.5 5.5 6.5
var3 = 7 8.5 9
...
varX = 10.0 11 12.0
IGNORE THIS LINE
IGNORE THIS LINE
IGNORE THIS LINE
var4 = 99
var5 = B
var6 = 0
IGNORE THIS LINE
IGNORE THIS LINE
IGNORE THIS LINE
v = 0
longvarname = 100
var whitespace = 0
main.cpp
int main (){
std::ifstream myfile1 ("inputfile.dat");
if (myfile1.is_open()){
myfile1.ignore(256, '\n');
myfile1.ignore(256, '\n');
myfile1.ignore(256, '\n');
myfile1.ignore(256, '\n');
myfile1.ignore(256, '\n');
myfile1.ignore(256, '=');
myfile1 >> var1_1 >> var1_2 >> var1_3;
myfile1.ignore(256, '=');
myfile1 >> var2_1 >> var2_2 >> var2_3;
myfile1.ignore(256, '=');
myfile1 >> var3_1 >> var3_2 >> var3_3;
myfile1.ignore(256, '=');
...
myfile1.ignore(256, '=');
myfile1 >> varX_1 >> varX_2 >> varX_3;
myfile1.ignore(256, '\n');
myfile1.ignore(256, '\n');
myfile1.ignore(256, '\n');
myfile1.ignore(256, '\n');
myfile1.ignore(256, '=');
myfile1 >> var4;
myfile1.ignore(256, '=');
myfile1 >> var5;
myfile1.ignore(256, '=');
myfile1 >> var6;
myfile1.ignore(256, '\n');
myfile1.ignore(256, '\n');
myfile1.ignore(256, '\n');
myfile1.ignore(256, '\n');
myfile1.ignore(256, '=');
myfile1 >> v;
myfile1.ignore(256, '=');
myfile1 >> longvarname;
myfile1.ignore(256, '=');
myfile1 >> var_whitespace;
}
else{
std::cerr << "ERROR! No access to inputfile.dat. Press ENTER to exit." << std::endl;
std::cin.get();
exit(1);
}
return 0
}
I've tried looking into getline() and splitting the line but I don't fully understand that. I don't want "strings" because all my variables are anything but a string (apart from one <char>).

Answer 1

I would scan this file line by line into a string.
Then try to see if that line contains a = in the line.
std::string line;
while (std::getline(myfile1), line)
{
if (line.find('=') != std::string::npos) {
handleImportant(line);
}
}
Now what you do with the line depends on your file definition.
It is not clear what your file definition is from the question.
Some lines have numbers, some have a set of numbers and one seems to have a character. It is unclear what is expected of the shown variables are the only variables.
But if we assume the simplist format:
<Variable Name> = <Some Text>
Then for each variable. We can store the associated text. We can split the text using a string stream.
std::map<std::string, std::string> variableMap;
void handleImportant(std::string const& line)
{
std::stringstream lineStream(line);
std::string variable;
char assign = 'X';
if (lineStream >> variable >> assign && assign == '=') {
// The rest of the line
// Or you can try and break up the line and convert
// to a specific type.
std::string restOfLine;
std::getline(lineStream, restOfLine);
variableMap[variable] = restOfLine;
}
}

Answer 2

You want something like
std::string line;
std::getline(myfile1, line); // note: give myfile1 a more descriptive name
// easier-to-read code is easier-to-debug as well
std::istringstream tokenizer(line);
std::string key;
std::string value;
if (std::getline(tokenizer, key, '=') && std::getline(tokenizer, value)
{
// use key and value
// key and value will be raw string data, whitespace and all, and
// will certainly require some amount of massaging into a more usable
// form. Remy raises the point of trimming the whitespace in the comments
// and in this case the string of nymbers will likely need to be
// transformed into a vector of an actual numeric type.
}
Wrap this up into a function and call the function in a loop to consume the file.