I have a text file with many values inside, and I want to read this file. The each value is 20 characters in length, eg -5.3815657119783E-04
with minus is 20 characters, and 3.4684258817593E-02
with one whitespace before 3 is also 20 characters in lengh. In my original method, i want to use the std::stringstream
to realize this function, however stringstream
splits the values by whitespace.
Most of my data is connected together. Therefore, I want to read this file every 20 characters to form one value, which means I want to split the data by 20 characters by c++, then produce 1 D vector.
Here is the data file:
-5.3815657119783E-04-6.8673010013991E-01-7.5323285000788E-03
3.4684258817593E-02 7.8204534345607E-02-9.0749590089286E-21
-3.2288090365673E-01 9.1882352987172E-02-3.6568412172092E-01
-1.6851899589453E-13-3.6952158259739E-06-1.7702955653531E-07
-1.3297325992783E-06-5.9693615642877E-04-3.8099426849223E-08
3.4698984898706E-08-4.6509379769221E-12-2.2296405498928E-02
-5.2019999391601E-14-4.7969995006506E-08 5.6662120105254E-08
8.9017338669484E-08-2.9332683813429E-06 1.0647933483993E-06
-6.7543843798968E-05-2.1529934384702E-03 2.2028879943185E-05
1.1715465910941E+05-2.5234840649194E+05 1.2213290262328E+05
6.1143067398521E-03 1.0479815336955E-04 7.8911962315577E-08
7.2476042335761E-01 4.1208576787560E-03 0.0000000000000E+00
5.3389720849081E-03 8.4526321374548E-05 4.8860066505864E-08
7.1085208590414E-06 4.5249593432595E-01 4.1468076430511E-04
5.6630655497271E-10 4.0969474876063E-11 9.7240386803972E-05
6.5005706844622E-11 5.1549675717799E-04 8.1291425432847E-18
3.4017603643097E-07 4.4928090110890E-03 1.8886378497020E-10
6.2728934586839E-11 4.7522407515395E-08 3.3417538614997E-07
1.9670991535049E-07 1.9522239039334E-08 2.7359845813293E-18
My original codes in c++:
std::vector<double> value;
ifstream infile;
infile.open("test-file");
int start_line_ = 0;
while (!infile.eof())
{
string line;
getline(infile, line);
if(rows >= start_line_)
{
double number;
std::stringstream stream(line);
while(stream >> number)
{
value.push_back(number);
}
}
infile.close();
}
My codes will get some values connected together, because they are not separated by whitespace.
As you already have the line in a string:
for (int i = 0; i + 20 <= line.size(); i += 20) {
double number;
istringstream(line.substr(i, 20)) >> number;
value.push_back(number);
}
If you're trying to build a vector of doubles, based on 20 character strings in the input file you could do this:
#include <iostream>
#include <fstream>
#include <vector>
#include <string>
#include <sstream>
int main()
{
std::vector<double> values;
std::ifstream infile;
infile.open("test-file");
std::string line;
// Read each line into a string
while (std::getline(infile, line))
{
// Iterate every 20 chars in the current line
for (size_t i = 0; i < line.size(); i += 20) {
// Get 20 char substring from current position,
// put into a stringstream
std::istringstream os(line.substr(i, 20));
// Put the stringstream into a double and push this to the values vector
double d;
os >> d;
values.push_back(d);
}
}
infile.close();
// Print them to check
for (auto& el : values)
std::cout << el << '\n';
return 0;
}
Loop through each line in the input, breaking the line into 20 char substrings.
Convert each substring to a double by means of std::istringstream os
and push this to the std::vector<double>
.
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