Checking if String is an int [duplicate] - c++

Question

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How to determine if a string is a number with C++?
(36 answers)
Closed 4 years ago.
I'm trying to enter the format of
"prog1 1 all file1"
the first input has to be a argv[1] should be an int.
So i need a way to determine if argv[1] is entered as a string "xxx" ( "prog1 xxx" ) it should return "NO PHRASE LENGTH" but its returning "INVALID PHRASE LENGTH".
I see there is a isdigit() function but im not sure how i would use that.
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

Your code is quite confusing. I am not sure what you were doing with the for loop to open the file. Anyway, I have given an example of what it could be.
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

Don't use std::endl when all you want to say is '\n' (or "...\n"). std::endl not only inserts a newline into the stream but also flushes it. If you *really* want to flush a stream be explicit and use std::flush.
Don't use exit() to end a program if there are other ways to do so. If you use exit() no stack unwinding will occur.
#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;
}
}
}