C++ Parsing char array as a script file (syntax) - c++

Question

I have made a simple Script reading class in C++ which allows me to read and parse scripts.
Basically there's a FILE class, which then I proceed to open with "fopen".
In functions I proceed to call "fgetc" and "ftell" to parse the script file as needed, note this ain't an interpreter.
Every script file is supposed to follow a syntax, but this is why I'm asking here for a solution.
Here's how a script looks like:
# Script File Comment
USERNAME = "Joe"
PASSWORD = "pw0001"
ACCESSLEVEL = 3
DATABASE = ("localhost",3306,"db","user","password")
Basically I have a few functions:
// This function searches for "variables"
nextToken();
// After I have the variable, e.g: USERNAME, PASSWORD, ACCESSLEVEL or DATABASE
// I proceed to call this function
// This function reads the char array for (,-{}()[]=) these are symbols
readSymbol();
// In a condition I check what "token/variable" I got and proceed to read
// it accordingly
// e.g; for USERNAME I do:
readString(); // reads text inside "
// e.g; for ACCESSLEVEL I do:
readNumber(); // reads digits until the next char ain't a digit
// e.g; for DATABASE I do:
readSymbol(); // (
readString(); // 127.0.0.1
readSymbol(); // ,
readNumber(); // 3306
readSymbol(); // ,
readString(); // db
readSymbol(); // ,
readString(); // user
readSymbol(); // ,
readString(); // password
readSymbol(); // )
I would like to be able to read a variable declaration like this:
DATABASELIST = {"data1","data2","data3"}
or
DATABASELIST = {"data1"}
I could easily do readSymbol and readString to read for 3 different string definitions inside the variable, however this list is supposed to have custom user data, like 5 different strings, or 8 different strings - depends.
And I seriously have no idea how can I do this with the parser I wrote.
Please note that I am basing this in some Pseudo code I took from a scripter for this type of format, I have the pseudo code extracted from IDA, if you would like to see it for better understanding post here
Here's an example of my "readSymbol" function.
READSYMBOL
int TReadScriptFile::readSymbol()
{
int currentData = 0;
int stringStart = -1;
// Check if we can't read anymore
if (end)
return 0;
while (true)
{
// Basically get chars in the script
currentData = fgetc(File);
// Check for end of file
if (currentData == -1)
{
end = true;
break;
}
if (stringStart == -1)
{
if (isdigit(currentData) || isalpha(currentData))
{
printf("TReadScriptFile::readSymbol: Symbol expected\n");
close();
return 0;
}
else if
(
currentData == '=' || currentData == ',' ||
currentData == '(' || currentData == ')' ||
currentData == '{' || currentData == '}' ||
currentData == '>' || currentData == '<' ||
currentData == ':' || currentData == '-'
)
{
#ifdef __DEBUG__
printf("Symbol: %c\n", currentData);
#endif
stringStart = ftell(File);
break;
}
}
}
return 1;
}
NEXTTOKEN
int TReadScriptFile::nextToken()
{
int currentData = 0;
int stringStart = -1;
int stringEnd = -1;
RecursionDepth = -1;
memset(String, 0, 4000);
// Check if we can't read anymore
if (end)
return 0;
while (true)
{
// ** Syntax **
if (isdigit(getNext()) || getNext() == -1)
{
printf("No more tokens left.\n");
end = true;
close();
return 0;
}
// End
// Basically get chars in the script
currentData = fgetc(File);
// Check for end of file
if (currentData == -1)
{
end = true;
break;
}
// Syntax Checking Part, this really isn't needed but w/e
if (stringStart == -1)
{
if (currentData == '=' || isdigit(currentData))
{
printf("TReadScriptFile::nextToken: Syntax Error: string expected\n");
close();
return 0;
}
}
// End Syntax Checking
// It's a comment line, we should skip
if (currentData == '#')
{
seekNewLn();
continue;
}
// There are no variables, yet
if (stringStart == -1)
{
// We found a letter, we are near a token!
if (isalpha(currentData))
{
stringStart = ftell(File);
// We might as well add the letter to the string
RecursionDepth++;
String[RecursionDepth] = currentData;
continue;
}
}
else if (stringStart != -1)
{
// Let's wait until we get an identifier or space
// We found a digit, error
if (isdigit(currentData))
{
printf("TReadScriptFile::nextToken: string expected\n");
close();
return 0;
}
// We found a space, maybe we should stop looking for tokens?
else if (isspace(currentData))
{
#ifdef __DEBUG__
printf("Token: %s\n", String);
#endif
break;
}
RecursionDepth++;
String[RecursionDepth] = currentData;
}
}
return 1;
}
I found a good example of the approach I followed here:
http://llvm.org/docs/tutorial/LangImpl1.html

Answer 1

One mechanism to deal with DATABASE_LIST would be this:
After finding the variable DATABASE_LIST read a symbol using readSymbol() checking if it is a { then in a loop do readString() add it to a std::vector (or some other suitable container) then check for a , or } (using readSymbol()) . If it is a ,(comma) then you go back and read another string add to the vector etc. until you do finally reach } . When you are finished you'd have a vector (dynamic array) of strings that represent a DATABASE_LIST