Checking command line inputs for errors in C++ - c++

Question

I had this program working just a bit ago but changed something and now my error handling has gone bonkers. I'm practically hitting my head against the wall here trying to put it back the way it was, but no matter what I do now, it spits out an error.
The program is supposed to take command line arguments to define the rows and columns and create a dynamic 2D array based on that. The format is "-rows (number) -columns (number)". I tried to add a few more cases before I turned in the assignment, but I must have changed some logic elsewhere, because even after I removed the new part it still won't work no matter what I input. At this point I think I just need a pair of fresh eyes to point me in the right direction.
int main(int argc, char* argv[]) {
// Checks if the user input the correct number of arguments.
// If so, checks if they were input corecctly. If so, it assigns
// the user input values to rows/columns, and if not, prints
// an error message.
if(argc == 5) {
for(int i = 1; i < argc; i++) {
rows = getArg(argc, argv, i, compare1);
}
for(int i = 1; i < argc; i++) {
columns = getArg(argc, argv, i, compare2);
}
} else {
printError(argv);
}
That is the relevant part of main.
Below are the functions involved in checking for errors. The one I actually have been working on is getArg, so I'm assuming this is where the logic is failing, but I included the other necessary function for clarity.
// Description: Checks if user input was valid
// Parameters: Command line arguments, int i from the for
// loop used to run this check on all command line arguments
// in main, and an array of chars used to compare the user's
// inputs to "-rows" or "-columns"
// Return value: If user input was valid, returns an int
// If not, exits program.
int getArg(int argc, char* argv[], int i, char compare[]) {
int arg;
if (strcmp(argv[i], compare) == 0) {
if (isInt((i + 1), argv)) {
arg = atoi(argv[i + 1]);
} else {
printError(argv);
}
} else {
printError(argv);
}
return arg;
}
// Description: Checks user input for valid integers
// Parameters: Command line arguments
// Return value: Returns true if input is an int;
// false if not.
bool isInt(int argc, char* argv[]) {
bool isInt;
for (int j = 0; j < strlen(argv[argc]); j++) { //For loop runs through each char in the array at argc
if (isdigit(argv[argc][j])) { // Checks to see if char is an integer
isInt = true;
return isInt;
} else {
isInt = false; // If there is ever a non-integer character, exit loop and return false
return isInt;
}
}
}

Answer 1

The first for loop in main continues to scan the argument list after it has matched "-rows". The loop makes the following calls (I'm assuming compare1="-rows" here since you didn't mention it):
i=1: getArg(argc=5, argv={"a.out", "-rows", "2", "-columns", "3"}, i=1, compare="-rows")
returns 2
i=2: getArg(argc=5, argv={"a.out", "-rows", "2", "-columns", "3"}, i=2, compare="-rows")
calls printError(argv) because strcmp("2", "-rows") is nonzero
Also, as Abhishek mentioned, isInt only ever checks the first character of the string because you return in the isInt = true branch.

Answer 2

One possible error that I can spot is that you are not looping correctly in your isInt() function.
You would invariably return out of the function after the 1st iteration.

Answer 3

Its nice you got an answer, but this is one is pretty easy to use and on entire SO you'll find this suggestion wherever such questions are tagged for C++
Using boost::program_options
#include <iostream>
#include <boost/program_options.hpp>
namespace po = boost::program_options;
int main( int argc, char *argv[ ] )
{
try {
int rows,cols;
po::options_description desc("Allowed options");
desc.add_options()
( "help", "produce this help message" )
( "rows", po::value< int>(&rows)->required(), "No. of Rows" )
( "cols", po::value< int>(&cols)->required(), "No. of Cols" )
;
po::variables_map vm;
po::store( po::parse_command_line( argc, argv , desc ), vm );
po::notify( vm );
if ( vm.count( "help" ) )
{
std::cout << desc;
return 0;
}
std::cout<<"Rows :"<<rows<<" "<<"Cols :"<<cols<<std::endl;
}
catch( std::exception& e )
{
std::cout << e.what() << "\n";
return 1;
}
return 0;
}
Usage :
./test --cols 4 --rows 3
Outputs :
Rows :3 Cols :4
Good Tutorial Here