Parsing CSV with String Streams

Yes, you can use string streams to parse comma-separated values (CSV) in C++. String streams (std::istringstream) are particularly useful for breaking down a CSV line into individual values.

Basic Example

Here’s a basic example to parse a single line of CSV:

1#include <iostream>
2#include <sstream>
3#include <vector>
4
5std::vector<std::string> ParseCSVLine(
6  const std::string& line
7) {
8  std::vector<std::string> result;
9  std::istringstream Stream(line);
10  std::string value;
11
12  while (std::getline(Stream, value, ',')) {
13    result.push_back(value);
14  }
15
16  return result;
17}
18
19int main() {
20  std::string line = "name,age,city";
21  std::vector<std::string> values =
22    ParseCSVLine(line);
23
24  for (const auto& value : values) {
25    std::cout << value << "\n";
26  }
27}

1name
2age
3city

In this example, std::getline() reads from the stream until it encounters a comma, extracting each value into the value variable. These values are then stored in a std::vector.

Parsing Multiple Lines

To parse multiple lines of CSV data, you can read each line from the input and process it using the ParseCSVLine function:

1#include <iostream>
2#include <sstream>
3#include <vector>
4
5using CSVLine = std::vector<std::string>;
6using CSVFile = std::vector<CSVLine>;
7
ParseCSVLine Function|Show
8CSVLine ParseCSVLine(const std::string&) {/*...*/}
20
21CSVFile ParseCSV(
22    const std::string& data) {
23  CSVFile result;
24  std::istringstream Stream(data);
25  std::string line;
26
27  while (std::getline(Stream, line)) {
28    result.push_back(ParseCSVLine(line));
29  }
30
31  return result;
32}
33
34int main() {
35  std::string data =
36    "name,age,city\nAlice,30,New York\n"
37    "Bob,25,Los Angeles";
38  CSVFile rows =
39    ParseCSV(data);
40
41  for (const auto& row : rows) {
42    for (const auto& value : row) {
43      std::cout << value << " ";
44    }
45    std::cout << "\n";
46  }
47}

1name age city
2Alice 30 New York
3Bob 25 Los Angeles

Handling Edge Cases

When parsing CSV data, you may encounter cases where values contain commas or are enclosed in quotes. Handling these edge cases requires additional parsing logic. For simplicity, here’s a basic approach without handling quoted values:

1CSVLine ParseCSVLine(const std::string& line) {
2  std::vector<std::string> result;
3  std::istringstream Stream(line);
4  std::string value;
5
6  while (std::getline(Stream, value, ',')) {
7    // Trim spaces from value
8    value.erase(0, value.find_first_not_of(' '));
9    value.erase(value.find_last_not_of(' ') + 1);
10    result.push_back(value);
11  }
12
13  return result;
14}

Summary

• Basic Parsing: Use std::getline() with a string stream to parse CSV lines.
• Multiple Lines: Process each line of the CSV data individually.
• Edge Cases: Handle special cases like quoted values and embedded commas with additional parsing logic.

Using string streams for parsing CSV is a powerful technique for simple and complex data processing tasks.