c++ file io & splitting by separator
Solution 1
There is really nothing wrong with fscanf, which is probably the fastest solution in this case. And it's as short and readable as the python code:
FILE *fp = fopen("file.dat", "r");
int x, y, z;
std::vector<int> vx, vy, vz;
while (fscanf(fp, "%d, %d, %d", &x, &y, &z) == 3) {
vx.push_back(x);
vy.push_back(y);
vz.push_back(z);
}
fclose(fp);
Solution 2
There's no real need to use boost in this example as streams will do the trick nicely:
int main(int argc, char* argv[])
{
ifstream file(argv[1]);
const unsigned maxIgnore = 10;
const int delim = ',';
int x,y,z;
vector<int> vecx, vecy, vecz;
while (file)
{
file >> x;
file.ignore(maxIgnore, delim);
file >> y;
file.ignore(maxIgnore, delim);
file >> z;
vecx.push_back(x);
vecy.push_back(y);
vecz.push_back(z);
}
}
Though if I were going to use boost I'd prefer the simplicity of tokenizer to regex... :)
Solution 3
Something like:
vector<int> inint;
vector<int> inbase;
vector<int> outbase;
while (fgets(buf, fh)) {
char *tok = strtok(buf, ", ");
inint.push_back(atoi(tok));
tok = strtok(NULL, ", ");
inbase.push_back(atoi(tok));
tok = strtok(NULL, ", ");
outbase.push_back(atoi(tok));
}
Except with error checking.
Solution 4
why not the same code as in python :) ?
std::ifstream file("input_hard.dat");
std::vector<int> inint, inbase, outbase;
while (file.good()){
int val1, val2, val3;
char delim;
file >> val1 >> delim >> val2 >> delim >> val3;
inint.push_back(val1);
inbase.push_back(val2);
outbase.push_back(val3);
}
Solution 5
If you don't mind using the Boost libraries...
#include <string>
#include <vector>
#include <boost/lexical_cast.hpp>
#include <boost/regex.hpp>
std::vector<int> ParseFile(std::istream& in) {
const boost::regex cItemPattern(" *([0-9]+),?");
std::vector<int> return_value;
std::string line;
while (std::getline(in, line)) {
string::const_iterator b=line.begin(), e=line.end();
boost::smatch match;
while (b!=e && boost::regex_search(b, e, match, cItemPattern)) {
return_value.push_back(boost::lexical_cast<int>(match[1].str()));
b=match[0].second;
};
};
return return_value;
}
That pulls the lines from the stream, then uses the Boost::RegEx library (with a capture group) to extract each number from the lines. It automatically ignores anything that isn't a valid number, though that can be changed if you wish.
It's still about twenty lines with the #include
s, but you can use it to extract essentially anything from the file's lines. This is a trivial example, I'm using pretty much identical code to extract tags and optional values from a database field, the only major difference is the regular expression.
EDIT: Oops, you wanted three separate vectors. Try this slight modification instead:
const boost::regex cItemPattern(" *([0-9]+), *([0-9]+), *([0-9]+)");
std::vector<int> vector1, vector2, vector3;
std::string line;
while (std::getline(in, line)) {
string::const_iterator b=line.begin(), e=line.end();
boost::smatch match;
while (b!=e && boost::regex_search(b, e, match, cItemPattern)) {
vector1.push_back(boost::lexical_cast<int>(match[1].str()));
vector2.push_back(boost::lexical_cast<int>(match[2].str()));
vector3.push_back(boost::lexical_cast<int>(match[3].str()));
b=match[0].second;
};
};
darudude
Updated on July 29, 2022Comments
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darudude almost 2 years
I have a file with data listed as follows:
0, 2, 10 10, 8, 10 10, 10, 10 10, 16, 10 15, 10, 16 17, 10, 16
I want to be able to input the file and split it into three arrays, in the process trimming all excess spaces and converting each element to integers.
For some reason I can't find an easy way to do this in c++. The only success I've had is by inputting each line into an array, and then regexing out all the spaces and then splitting it up. This entire process took me a good 20-30 lines of code and its a pain to modify for say another separator(eg. space), etc.
This is the python equivalent of what I would like to have in C++:
f = open('input_hard.dat') lines = f.readlines() f.close() #declarations inint, inbase, outbase = [], [], [] #input parsing for line in lines: bits = string.split(line, ',') inint.append(int(bits[0].strip())) inbase.append(int(bits[1].strip())) outbase.append(int(bits[2].strip()))
The ease of use of doing this in python is one of the reasons why I moved to it in the first place. However, I require to do this in C++ now and I would hate to have to use my ugly 20-30 line code.
Any help would be appreciated, thanks!
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MattyT over 15 yearsI would avoid such a "C-ish" solution for, well, aesthetics...but more importantly in this case because strtok has some serious thread-safe issues. Correct code though!
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jbruni over 11 yearsNice job. Folks forget about scanf's pattern matching. The simplest solution is the best.