How to limit the number of characters per line in a string without separating the characters of the-CodePudding

I am trying to write a code that ensures that the number of characters per line are at the most 80 without separating words (it will be stored in a txt file). I'm not really sure what type of c functions will help me do that.

CodePudding user response：

Your question is way too broad and there are many ways to answer it, but here is an intuitive and easy-to-read one, it's neither optimized for performance nor for memory-safe operations but rather for the sake of understanding how to write an algorithm.

    std::vector<std::string> lines;
    std::string text = "The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog.";

    const size_t lineLimit = 80;
    size_t lastOffset = 0;

    while (lastOffset < text.size() - lineLimit)
    {
        // find the next blank space index,
        // -1 is because the offset starts at zero
        size_t nextSpace = text.find(" ", lastOffset   lineLimit - 1);

        // if there aren't any blank spaces left, break the loop
        if (nextSpace == -1) break;

        // add a line of text from text[lastOffset] to text[nextSpace]
        lines.push_back(std::string(text.data()   lastOffset, nextSpace - lastOffset));

        // we need to add 1 to skip the blank
        // space right after the text[nextSpace]
        lastOffset = nextSpace   1;
    }

    // add anything left in the buffer as the last line
    lines.push_back(std::string(text.data()   lastOffset));

    for (std::string& line : lines)
    {
        std::cout << line << '\n';
    }

CodePudding user response：

You could just read each line into a std::string and then search for whitespace characters in the first 80 characters, starting from the 80:th character. If a whitespace is found, take the substring of that part - else, you'll have to break at 80 even though it's within a word.

Example:

#include <algorithm>
#include <cctype>
#include <iostream>
#include <string>

int main() {
    constexpr size_t max_len = 80;
    std::string line;

    while (std::getline(std::cin, line)) {
        while (line.size() > max_len) { // longer than max_len, try to find a space
            auto it =
                std::find_if(line.rend() - max_len, line.rend(),
                             [](unsigned char ch) { return std::isspace(ch); });

            if (it != line.rend()) { // space found in the first max_len characters
                auto len = std::distance(it, line.rend());
                std::cout << line.substr(0, len - 1) << "\n";
                line = line.substr(len);

            } else { // no space found - break at max_len
                std::cout << line.substr(0, max_len) << '\n';
                line = line.substr(max_len);
            }
        }
        std::cout << line << '\n';
    }
}