I'm currently beginning on C++ and trying to make a function that can open a .txt file, read it, and save its words in an array (each word being a protein sequence). Unfortunately I don't succeed at calling the argument containing the name of the file ( argv[1]
) in the function. Can anyone spot errors in my code or in the way I implemented this ? Thanks in advance, you will find the code and the error messages below :
So here are my librairies and 'shortcuts'.
// Librairies
#include <iostream>
#include <string>
#include <fstream>
// Alias
using std::cout;
using std::endl;
using std::string;
Now this is the function, note that filename is supposed to be a string containing argv[1]
(the name of a .txt file specified at execution) :
string SequenceChoice(int n, string filename); // Function returning a string
std::ifstream sequenceFile (filename); //Opens the file specified on execution
if ( sequenceFile.is_open() )
{
cout<<"File opened"<<endl;
string tmp;
int i = 0;
while( sequenceFile >> tmp ) // Counts the number of sequences (words)
{
i++;
}
string allchains[i]; // Creates an array of strings, to save all the words
sequenceFile.clear();
sequenceFile.seekg(0, sequenceFile.beg); // Replaces the cursor at the beginning of the file
i=0;
while( sequenceFile >> allchains[i]) // Saves each word as a string in an array
{
cout << allchains[i] << tmp;
i++;
}
sequenceFile.close();
cout<< "File closed"<<endl;
}
else
{
cout << "Error: Cannot open file" << endl;
}
return allchains[n]; // returns the 'n'th word (n being specified when calling the function
// end of the function
Now the main function, I'm not sure if doing string filename = argv[1]
works, but I get less errors when I keep this step instead of putting argv[1]
as an argument of my SequenceChoice()
function.
int main(int argc, char *argv[]) {
if(argc >= 2)
{
string filename = argv[1];
cout << SequenceChoice( 2, filename ) << endl; // I expect it to give me the 3rd word of a .txt file for example.
}
else
{
cout << "Error : No file" << endl;
}
return 0;
}
The link above is a picture of the error message I get when I compile, I've been searching for hours on the internet how to resolve this, unfortunately I could'nt manage to have the code working. There's probably an error of type with the way I deal with argv[], but I failed at solving it so any help and comments would be greatly appreciated.
Please try changing following line
string SequenceChoice(int n, string filename); // Function returning a string
to
string SequenceChoice(int n, string filename) { // Function returning a string
You are trying to write a function but the ; is terminating your function and body is not starting. It should work. Also please read a book carefully.
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Try this :
string SequenceChoice(int n, string filename)
{
std::ifstream sequenceFile (filename); //Opens the file specified on execution
if ( sequenceFile.is_open() )
{
cout<<"File opened"<<endl;
string tmp;
int i = 0;
while( sequenceFile >> tmp ) // Counts the number of sequences (words)
{
i++;
}
string allchains[i]; // Creates an array of strings, to save all the words
sequenceFile.clear();
sequenceFile.seekg(0, sequenceFile.beg); // Replaces the cursor at the beginning of the file
i=0;
while( sequenceFile >> allchains[i]) // Saves each word as a string in an array
{
cout << allchains[i] << tmp;
i++;
}
ifs.close();
cout<< "File closed"<<endl;
}
else
{
cout << "Error: Cannot open file" << endl;
}
return allchains[n];
}
Here is fully functioning code: You can compare it with yours.
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
string SequenceChoice(int n, string filename){ // Function returning a string
std::ifstream sequenceFile (filename); //Opens the file specified on execution
if ( sequenceFile.is_open() )
{
cout<<"File opened"<<endl;
string tmp;
int i = 0;
while( sequenceFile >> tmp ) // Counts the number of sequences (words)
{
i++;
}
string allchains[i]; // Creates an array of strings, to save all the words
sequenceFile.clear();
sequenceFile.seekg(0, sequenceFile.beg); // Replaces the cursor at the beginning of the file
i=0;
while( sequenceFile >> allchains[i]) // Saves each word as a string in an array
{
cout << allchains[i] << tmp;
i++;
}
sequenceFile.close();
cout<< "File closed"<<endl;
return allchains[n]; // returns the 'n'th word (n being specified when calling the function
}
else
{
cout << "Error: Cannot open file" << endl;
}
return NULL;
// end of the function
}
int main(int argc, char *argv[])
{
if(argc >= 2)
{
string filename = argv[1];
cout << SequenceChoice( 2, filename ) << endl; // I expect it to give me the 3rd word of a .txt file for example.
}
else
{
cout << "Error : No file" << endl;
}
}
Thanks to your answers I managed to solve my problem, apart from some syntax errors in the code the argument filename
in the function was a string, and as argv[]
is an array of pointers. So it just couldn't work to consider them as the same type.
Here is a working version of the function, for those it could help :
string SequenceChoice(int n, char* argv[])
{
std::ifstream sequenceFile (argv[1]); //Opens the file specified on execution
if ( sequenceFile.is_open() )
{
cout<< " .File opened. \n" <<endl;
string tmp;
int i = 0;
while( sequenceFile >> tmp ) // Counts the number of sequences (words)
{
i++;
}
cout << " " << i << " chains in the .txt file : \n" << endl;
string allchains[i]; // Creates an array of strings, to save all the words
sequenceFile.clear();
sequenceFile.seekg(0, sequenceFile.beg); // Replaces the cursor at the beginning of the file
i=0;
while( sequenceFile >> allchains[i]) // Saves each word as a string in an array
{
cout << " --- Chain "<< i + 1 << " --- : " << allchains[i] << endl;
i++;
}
sequenceFile.close();
cout << "\n .File closed. \n" << endl;
return allchains[n];
}
else
{
cout << "Error: Cannot open file" << endl;
return NULL;
}
}
And finally the new main function :
int main(int argc, char *argv[]) {
if(argc >= 2)
{
string filename = argv[1];
cout << SequenceChoice( 2, argv ) << endl; // Shows the 3rd word of the file, as an example.
}
else
{
cout << "Error : No file" << endl;
}
return 0;
}
Thanks for your help and have a great day !
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