如果程序被指定像这样运行,那么在c++中解析命令行参数的最佳方式是什么:

prog [-abc] [input [output]]

是否有某种方法可以在标准库中实现这一点,或者我需要自己编写代码?


相关:

在unicode c++应用程序中解析命令行参数


当前回答

AnyOption是一个c++类,用于轻松解析复杂的命令行选项。它还以选项值对格式解析来自rsourcefile的选项。

AnyOption实现了传统的POSIX风格的字符选项(-n)以及较新的GNU风格的长选项(——name)。或者您可以通过要求忽略POSIX样式选项来使用更简单的长选项版本(-name)。

其他回答

Following from my comment and from rbaleksandar's answer, the arguments passed to any program in C are string values. You are provided the argument count (argc) which gives you the argument indexes zero-based beginning with the name of the program currently being run (which is always argv[0]). That leaves all arguments between 1 - argc as the user supplied arguments for your program. Each will be a string that is contained in the argument vector (which is a pointer to an array of strings you will seen written as char *argv[], or equivalently as a function parameter char **argv) Each of the strings argv[1] to argv[argc-1] are available to you, you simply need to test which argument is which.

这将允许您分离,并使它们可用为命令(cmd),选项(opt)和最后的参数(arg)到您的cmd。

Now it is worth noting, that the rules of your shell (bash, etc..) apply to the arguments passed to your program, word-splitting, pathname and variable expansion apply before your code gets the arguments. So you must consider whether single or more commongly double-quoting will be required around any of your arguments to prevent the normal shell splitting that would otherwise apply (e.g. ls -al my file.txt would results in 4 user-supplied arguments to your code, while ls -al "my file.txt" or ls -al my\ file.txt which would result in the 3 your were expecting.

把所有这些放在一起,您的简短解析可以像下面这样完成。(你也可以自由地做你喜欢的,使用一个开关而不是嵌套的if等…)

#include <stdio.h>

int main (int argc, char **argv) {

    char *cmd = NULL,   /* here, since you are using the arguments  */
         *opt = NULL,   /* themselves, you can simply use a pointer */
         *arg = NULL;   /* or the argument itself without a copy    */

    /* looping using the acutal argument index & vector */
    for (int i = 1; i < argc; i++) {
        if (*argv[i] != '-') {      /* checking if the 1st char is - */
            if (!cmd)               /* cmd is currently NULL, and    */
                cmd = argv[i];      /* no '-' it's going to be cmd   */
            else                    /* otherwise, cmd has value, so  */
                arg = argv[i];       /* the value will be opt        */
        }
        else                /* here the value has a leading '-', so  */
            opt = argv[i];  /* it will be the option */
    }

    printf ("\n cmd : %s\n opt : %s\n arg : %s\n\n",
            cmd, opt, arg);

    return 0;
}

使用/输出示例

如果你运行代码,你会发现它为参数提供了分离,并提供了单独的指针,以方便它们的使用:

$ ./bin/parse_cmd ls -la ./cs3000

 cmd : ls
 opt : -la
 arg : ./cs3000

(需要注意的是,如果你的任务是构建一个命令字符串,你需要复制多个值来表示opt或arg,那么你不能再简单地使用指针,而需要创建存储,要么通过简单的数组声明而不是指针开始,或者你可以根据需要动态分配存储,例如malloc, calloc和/或realloc。然后,您将有可用的存储空间来复制和连接其中的值。)

如果这是你的挑战,那么在所有这些答案之间,你应该知道如何处理你的问题。如果你必须更进一步,实际上让你的程序执行带有opt和arg的cmd,那么你会想要查看fork来生成一个半独立的进程,在其中运行将执行你的cmd opt和arg,使用类似于execv或execvp的东西。祝你好运,如果你有进一步的问题,请发表评论。

它太大了,不可能包含在Stack Overflow回答中,但我创建了一个用于声明式定义命令行的库。它利用了c++ 14通过给每个成员变量赋初始值来构建类构造函数的能力。

这个库基本上是一个基类。要定义命令语法,需要声明一个派生自该语法的结构。下面是一个例子:

struct MyCommandLine : public core::CommandLine {
    Argument<std::string> m_verb{this, "program", "program.exe",
        "this is what my program does"};
    Option<bool> m_help{this, "help", false,
        "displays information about the command line"};
    Alias<bool> alias_help{this, '?', &m_help};
    Option<bool> m_demo{this, "demo", false,
        "runs my program in demonstration mode"};
    Option<bool> m_maximize{this, "maximize", false,
        "opens the main window maximized"};
    Option<int> m_loops{this, "loops", 1,
        "specifies the number of times to repeat"};
    EnumOption<int> m_size{this, "size", 3,
                           { {"s", 1},
                             {"small", 1},
                             {"m", 3},
                             {"med", 3},
                             {"medium", 3},
                             {"l", 5},
                             {"large", 5} } };
    BeginOptionalArguments here{this};
    Argument<std::string> m_file{this, "file-name", "",
        "name of an existing file to open"};
} cl;

参数、选项和别名类模板是在CommandLine基类的范围内声明的,您可以为自己的类型专门化它们。每个选项都包含this指针、选项名称、默认值和用于打印命令概要/用法的描述。

我仍然在寻找消除所有这些指针的需要,但我还没有找到一种不引入宏的方法。这些指针允许每个成员向驱动解析的基类中的表注册自己。

一旦有了实例,就会有多个方法重载来解析来自字符串或主样式参数向量的输入。解析器同时处理windows风格和unix风格的选项语法。

if (!cl.Parse(argc, argv)) {
    std::string message;
    for (const auto &error : cl.GetErrors()) {
        message += error + "\n";
    }
    std::cerr << message;
    exit(EXIT_FAILURE);
}

一旦它被解析,你可以使用operator()访问任何选项的值:

if (cl.m_help()) { std::cout << cl.GetUsage(); }
for (int i = 0; i < cl.m_loops(); ++i) { ... }

整个库只有大约300行(不包括测试)。实例有点臃肿,因为解析表是实例(而不是类)的一部分。但是每个程序通常只需要一个实例,而且这种纯声明性方法的便利性非常强大,可以通过解析新输入简单地重置实例。

提高program_options。

如果你不想使用boost,我推荐这个小助手类。

我可以建议使用模板化的c++命令行解析器库(GitHub上的一些分支是可用的),API非常直接并且(引用自网站):

该库完全在头文件中实现,因此很容易 与其他软件一起使用和分发。它是MIT授权的 无后顾之忧的发行许可证。

这是手册中的一个例子,为了简单起见,这里有颜色:

#include <string>
#include <iostream>
#include <algorithm>
#include <tclap/CmdLine.h>

int main(int argc, char** argv)
{

    // Wrap everything in a try block.  Do this every time,
    // because exceptions will be thrown for problems.
    try {

    // Define the command line object, and insert a message
    // that describes the program. The "Command description message"
    // is printed last in the help text. The second argument is the
    // delimiter (usually space) and the last one is the version number.
    // The CmdLine object parses the argv array based on the Arg objects
    // that it contains.
    TCLAP::CmdLine cmd("Command description message", ' ', "0.9");

    // Define a value argument and add it to the command line.
    // A value arg defines a flag and a type of value that it expects,
    // such as "-n Bishop".
    TCLAP::ValueArg<std::string> nameArg("n","name","Name to print",true,"homer","string");

    // Add the argument nameArg to the CmdLine object. The CmdLine object
    // uses this Arg to parse the command line.
    cmd.add( nameArg );

    // Define a switch and add it to the command line.
    // A switch arg is a boolean argument and only defines a flag that
    // indicates true or false.  In this example the SwitchArg adds itself
    // to the CmdLine object as part of the constructor.  This eliminates
    // the need to call the cmd.add() method.  All args have support in
    // their constructors to add themselves directly to the CmdLine object.
    // It doesn't matter which idiom you choose, they accomplish the same thing.
    TCLAP::SwitchArg reverseSwitch("r","reverse","Print name backwards", cmd, false);

    // Parse the argv array.
    cmd.parse( argc, argv );

    // Get the value parsed by each arg.
    std::string name = nameArg.getValue();
    bool reverseName = reverseSwitch.getValue();

    // Do what you intend.
    if ( reverseName )
    {
            std::reverse(name.begin(),name.end());
            std::cout << "My name (spelled backwards) is: " << name << std::endl;
    }
    else
            std::cout << "My name is: " << name << std::endl;


    } catch (TCLAP::ArgException &e)  // catch any exceptions
    { std::cerr << "error: " << e.error() << " for arg " << e.argId() << std::endl; }
}