Converting char* to an array of strings by splitting

Question

I want to convert a char* line of commands into a string array. What I tried:

void parse(char* cmd, int length) {
    std::string *arguments = nullptr;
    int amount = 0;
    for (int i = 0; i < length; i++) {
        if (cmd[i] == ' ' || cmd[i] == '\t' || cmd[i] == '\n') {
            amount++;
            continue;
        }
        arguments[amount] = cmd[i];
    }
}

But I'm not sure about the std::string *arguments = nullptr; part. I don't know the amount of arguments in the cmd so I'm not sure how to initialize properly the arguments array. In C I probably should solve it with malloc but how do I solve it in C++? Also, as I want to return arguments and amount, how can I pass them as arguments references to the parse string?

Prefer to use vector. Avoiding vector in C++ similar to avoiding memset and strcmp in C. — Mooing Duck
– Mooing Duck, Commented May 4, 2020 at 21:02
If your first thought is to use malloc in C, then your first though in C++ should be use use std::vector or std::unique_ptr — NathanOliver
– NathanOliver, Commented May 4, 2020 at 21:03
'How do I solve it in C++?' Use a vector of strings, std::vector<std::string> arguments;. Use push_back to add strings to the vector and push_back to add characters to the string. — john
– john, Commented May 4, 2020 at 21:03
Usage of std::istringstream and std::vector<std::string> makes this a trivial operation. — PaulMcKenzie
– PaulMcKenzie, Commented May 4, 2020 at 21:03

Remy Lebeau · Accepted Answer · 2020-05-04 21:21:12Z

4

You are not allocating any memory for arguments to point at. Use std::vector<std::string> instead of std::string*. Also see Splitting strings in C++.

Try something more like this:

#include <string>
#include <vector>
#include <cctype>

std::vector<std::string> parse(const char* cmd, int length) {
    std::vector<std::string> arguments;
    const char *start = cmd;
    const char *stop = cmd + length;
    while (start < stop) {
        while ((start < stop) && isspace(*start)) ++start;
        if (start == stop) break;
        const char *end = start + 1;
        while ((end < stop) && !isspace(*end)) ++end;
        arguments.push_back(std::string(start, end-start));
        start = end + 1;
    }
    return arguments;
}

Live Demo

Alternatively, operator>> handles whitespace parsing for you, so you can wrap the cmd data inside of a std::istringstream and loop through that instead, eg:

#include <string>
#include <vector>
#include <sstream>

std::vector<std::string> parse(char* cmd, int length) {
    std::vector<std::string> arguments;
    std:istringstream iss(std::string(cmd, length));
    std::string s;
    while (iss >> s) {
        arguments.push_back(s);
    }
    return arguments;
}

Live Demo

edited May 4, 2020 at 21:21

answered May 4, 2020 at 21:09

Remy Lebeau

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4 Comments

Slava Over a year ago

Type of the argument should be changed to const char *

vesii Over a year ago

Thank you! I'm trying to pass char* arguments[MAX]; but for some reason I get a mismatch. Do you know why?

Ted Lyngmo Over a year ago

@vesii That's an array of char* but your function takes a char*

Remy Lebeau Over a year ago

@vesii Are you trying to populate a char*[] array that you pass in, or are you trying to parse such an array? You need to be more specific. Please edit your question with more details.

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