Parsing input configuration files - Part 1

Hi,

When dealing with loading input configuration files, it is annoying to parse each line of the file and store the value in a parameter for each line. This often clutters the code due to the extensive if-else if-else if...-else statements for each config parameter. In the end this greatly affects the code maintainability. So let me introduce you a better approach to minimize the pain of maintenance.

Assumptions

I take it for granted that I'm addressing the audience who have their code in C++. I assume that you all might have stored the set of input parameters in a structure or a class, say ConfigStruct. If you haven't done so, I recommend encapsulating your input/output parameters in a nice structure atleast now. I use STL in this example to make things easier - you may also use your own version of the STL container if you are against using STL for some personal reasons.

Scenario: (existing parser logic)

If your input config parsing logic is something like,

if ( !strcmp(inputParam1,"paramStr1") ) {

load paramStr1's value into inputParam1

} else if ( !strcmp(inputParam2,"paramStr2") ) {

load paramStr2's value into inputParam2

} else {

print that the config parameter is unrecognized and probably quit

}

then you've come to the right place.

Pointer-based approach

This method deals with two forms of association:

a. Tying each config file tag to the datatype of corresponding variable - introduce a STL "map" called tagTypeMap

b. Tying each config file tag to the address of corresponding variable - introduce a STL "map" called tagAddrMap

Declaration of these maps

std::map<std::string,std::string> tagTypeMap;

std::map<std::string,void*> tagAddrMap;

New parser logic

registerConfig() {

#define REGISTER(tag,var) tagTypeMap[tag]=typeid(var).name();

REGISTER("paramStr1",inputParam1)

REGISTER("paramStr2",inputParam2)

//and so on.

#define REGISTER_ADDR(tag,var) tagAddrMap[tag]=(void*)&var;

REGISTER_ADDR("paramStr1",inputParam1)

REGISTER_ADDR("paramStr2",inputParam2)

//and so on.

}

parseTag() {

if ( tagTypeMap.find(tag) == tagTypeMap.end() )

return; //variable not found

std::string type = tagTypeMap.find(tag)->second;

if ( tagAddrMap.find(tag) == tagAddrMap.end() )

return; //addr not registered

void *vptr = tagAddrMap.find(tag)->second;

// If you include a new data type

// as input parameter, please define

// conversion for that data type in here

if ( type == typeid(std::string).name() ) {

std::string *ptr = (std::string*) vptr;

*ptr = value;

} else if ( type == typeid(int).name() ) {

int *ptr = (int*) vptr;

*ptr = atoi(value.c_str());

} else if ( type == typeid(float).name() ) {

float *ptr = (float*) vptr;

*ptr = atof(value.c_str());

} //and so on

}

I'll go over the second approach (template-based) in one of my future blogs (possibly the next one).

Until we meet again,

-Srini-