检查字符串是否为 int [重复]

Question

我正在尝试输入格式

"prog1 1 所有文件1"

第一个输入必须是 argv[1] 应该是 int。

所以我需要一种方法来确定 argv[1] 是否作为字符串“xxx”（“prog1 xxx”）输入，它应该返回“NO PHRASE LENGTH”但它返回“INVALID PHRASE LENGTH”。

我看到有一个 isdigit() 函数，但我不确定如何使用它。

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


try{
if(argc == 1){

   cout << "NO PHRASE LENGTH" << endl;  exit(1); 
}
else if((stoi(argv[1])) <= 0 ){ 

    cout << "INVALID PHRASE LENGTH" << endl;  exit(1); 
}
else if(argc == 2){

   cout << "NO MODE" << endl;  exit(1); 
}
else if(!(std::string(argv[2]) == "all") && !(std::string(argv[2]) == "top")){

    cout << "INVALID MODE" << endl;
}
else if(argc == 3){

    cout << "NO FILES GIVEN" << endl;
}
else if(argc >= 4){


    ifstream f;
    for(int i = 4; i < argc; i--){

        f.open( argv[i] );

        if( ! f.good() ) { 
            cout << "BAD FILE " << argv[i] << endl; exit(1); 
        }

        //cout << "OK" << endl;
        //f.close();

    }




}
else
    return 0;
}
catch(exception e){
}} 

Answer 1

您的代码非常混乱。我不确定你在用 for 循环做什么来打开文件。不管怎样，我已经举了一个例子。

int main(int argc, char *argv[])
{
    if(argc != 4)
    {
        cout << "Program requires 3 parameters!" << endl;
        return -1;
    }

    if(std::string(argv[2]) != "all" && std::string(argv[2]) != "top")
    {

        cout << "INVALID MODE" << endl;
        return -1;
    }

    try
    {
        if(stoi(argv[1]) < 1)
        {
            cout << "ZERO OR NEGATIVE PHRASE LENGTH" << endl;
            return -1;
        }

        ifstream f(argv[3]);
        if(!f) 
        { 
            cout << "BAD FILE " << argv[3] << endl;
            return -1; 
        }

        // Now do whatever you want with the opened file
    }
    catch(out_of_range e)
    {
        cout << "NON-INT PHRASE LENGTH" << endl; 
        return -1;
    }
    return 0;
} 

Answer 2

当你只想说'\n'（或"...\n"）时，不要使用std::endl。 std::endl 不仅在流中插入换行符，而且还刷新它。如果你*真的*想刷新一个流，请明确并使用std::flush。

如果有其他方法，请不要使用exit() 来结束程序。如果您使用exit()，则不会发生堆栈展开。

#include <cstdlib>
#include <string>
#include <iostream>
#include <exception>
#include <fstream>

int main(int argc, char **argv)
{
    if (argc == 1) {
        std::cerr << "NO PHRASE LENGTH\n";
        return EXIT_FAILURE;
    }

    if (argc == 2) {
        std::cerr << "NO MODE\n";
        return EXIT_FAILURE;
    }

    if (argc == 3) {
        std::cerr << "NO FILES GIVEN\n";
        return EXIT_FAILURE;
    }

    int phrase_length;
    try {
        phrase_length = std::stoi(argv[1]);
        if (phrase_length < 0)
            throw std::out_of_range{ nullptr };
    }
    catch (std::invalid_argument) {
        std::cerr << "NO PHRASE LENGTH";
        return EXIT_FAILURE;
    }
    catch (std::out_of_range) {
        std::cerr << "PHRASE LENGTH OUT OF RANGE\n";
        return EXIT_FAILURE;
    }

    std::string mode{ argv[2] };

    if ( mode != "all" && mode != "top") {
        std::cerr << "INVALID MODE\n";
        return EXIT_FAILURE;
    }

    for (int i = 3; i < argc; ++i) {
        std::fstream input_file{ argv[i] };
        if (!input_file.is_open()) {
            std::cerr << "BAD FILE \"" << argv[i] << "\"\n";
            return EXIT_FAILURE;
        }
    }
}