How to use part of a filename as a variable in C++ - c++

Question

I have a few thousand pcap files that I'm trying to parse as part of a research project. They are all named as xxx.xxx.xxx.xxx_yyy.yyy.yyy.yyy.pcap where the first IP address is the one I'm trying to use as a variable in my C++ program.
Parsing the pcap files themselves is not an issue. I am passing the filename to the function as a pointer and just don't quite know how to grab that first part of the filename.
As requested, here is a bit of code:
//program.cpp//
int main(int argc, char *argv[]){
char * inFile;
inFile = argv[1];
result = parsePkts(inFile);
return 0;
}
//functions.h//
int parsePkts(char *fn){
struct ip *ipHdr = NULL;
ipHdr = (struct ip *)(data + sizeof(struct ether_header));
if((ipHdr -> ip_dst.s_addr)) == xxx.xxx.xxx.xxx) {
do stuff
}
}
Obviously there is a lot more to the program but this is where I need to grab it. Thanks.

Answer 1

if your input is const char* as filename you can split it in severals ways. You wrote that you need to split it into some parts (first part). I have little snippet to split string by char in your case '_'
void stringSplitBy(std::string str, const char *separator, std::vector<std::string> &results)
{
size_t found = str.find_first_of(separator);
while (found != std::string::npos) {
if (found > 0) {
results.push_back(str.substr(0, found));
}
str = str.substr(found + 1);
found = str.find_first_of(separator);
}
if (str.length() > 0) {
results.push_back(str);
}
}
Use it in this way:
const char* inputfname = "xxx.xxx.xxx.xxx_yyy.yyy.yyy.yyy.pcap";
std::string fname = std::string(inputfname);
std::vector<std::string> results;
stringSplitBy(fname, '_', results);
You can print result:
std::vector<std::string>::iterator it = results.begin();
for (; it != results.end(); ++it)
{
std::cout<< (*it).c_str() << std::endl;
}