C ++比较并替换stringstream的最后一个字符 [英] C++ Compare and replace last character of stringstream

问题描述

我想检查以下内容：

1. 如果最后一个字符附加到 stringstream 是逗号。


2. 如果将其删除。

1. If the last character appended to the stringstream is a comma.
2. If it is remove it.

---

---

std::stringstream str;
str << "["
//loop which adds several strings separated by commas

str.seekp(-1, str.cur); // this is to remove the last comma before closing bracket

str<< "]";

问题是如果循环中未添加任何内容，则从字符串中删除开括号。因此，我需要一种方法来检查最后一个字符是否为逗号。我这样做是这样的：

The problem is if nothing is added in the loop, the opening bracket is removed from the string. So I need a way to check whether the last character is a comma. I did that like this:

if (str.str().substr(str.str().length() - 1) == ",")
{
    str.seekp(-1, rteStr.cur);
}

但是我对此不太满意。

But I don't feel very good about this. Is there a better way to do this?

关于循环：

循环用于标记集合通过套接字接收的命令集，并将其格式化以通过另一个套接字发送到另一个程序。每个命令以 OVER 标志结尾。

Loop is used to tokenize a set of commands received through sockets and format it to send to another program through another socket. Each command ends with an OVER flag.

std::regex tok_pat("[^\\[\\\",\\]]+");
std::sregex_token_iterator tok_it(command.begin(), command.end(), tok_pat);
std::sregex_token_iterator tok_end;
std::string baseStr = tok_end == ++tok_it ? "" : std::string(*tok_it);
while (baseStr == "OVER")
{
    //extract command parameters
    str << "extracted_parameters" << ","
}

推荐答案

我经常处理这些循环的方式，希望在这些循环中放置空格或空格项目之间的逗号 如下所示：

The way I often deal with these loops where you want to put something like a space or a comma between a list of items is like this:

int main()
{
    // initially the separator is empty
    auto sep = "";

    for(int i = 0; i < 5; ++i)
    {
        std::cout << sep << i;
        sep = ", "; // make the separator a comma after first item
    }
}

输出：

0, 1, 2, 3, 4

如果想提高速度效率，可以使用 if（ ），然后进入循环以输出其余的类似项：

If you want to make it more speed efficient you can output the first item using an if() before entering the loop to output the rest of the items like this:

int main()
{
    int n;

    std::cin >> n;

    int i = 0;

    if(i < n) // check for no output
        std::cout << i;

    for(++i; i < n; ++i) // rest of the output (if any)
        std::cout << ", " << i; // separate these
}

在您的情况下，第一个解决方案可以像此：

    std::regex tok_pat("[^\\[\\\",\\]]+");
    std::sregex_token_iterator tok_it(command.begin(), command.end(), tok_pat);
    std::sregex_token_iterator tok_end;
    std::string baseStr = tok_end == ++tok_it ? "" : std::string(*tok_it);

    auto sep = ""; // empty separator for first item

    while (baseStr == "OVER")
    {
        // extract command parameters
        str << sep << "extracted_parameters";
        sep = ","; // make it a comma after first item
    }

第二个（可能更节省时间）解决方案：

    std::regex tok_pat("[^\\[\\\",\\]]+");
    std::sregex_token_iterator tok_it(command.begin(), command.end(), tok_pat);
    std::sregex_token_iterator tok_end;
    std::string baseStr = tok_end == ++tok_it ? "" : std::string(*tok_it);

    if (baseStr == "OVER")
    {
        // extract command parameters
        str << "extracted_parameters";
    }

    while (baseStr == "OVER")
    {
        // extract command parameters
        str << "," << "extracted_parameters"; // add a comma after first item
    }

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