execvp won't work with cut - c++

Question

I'm making work to school and I have a problem with "cut" command when I try launch this command in c++. So this is my exercise-> I want launch this command in C++ -> "cut -d':' -f5 < file" I wrote text from the file to variable input in main function.
expected as result of command -> "five"
but I got only an error message "cut: the delimiter must be a single character
Try 'cut --help' for more information."
do you know why ? Thanks for help :)
this is my test code:
#include <iostream>
#include <sys/wait.h>
#include <unistd.h>
#include <string>
#include <cstdio>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <cstdlib>
const int BUFFER_SIZE = 4096;
using namespace std;
char *argCat[] = { "cat", (char *)0 };
char *argEcho[] = { "echo", "Hello", (char *)0 };
char *argCut[] = { "cut", "-d':'", "-f5", (char *)0};
char *stringCharConvertor(string paString)
{
char * temp = new char[paString.size() + 1];
std::copy(paString.begin(), paString.end(), temp);
temp[paString.size()] = '\0';
return temp;
}
void executeCommand(char** paCommand, string &paOutput, string &paInput)
{
char** arg = paCommand;
bool validInput = paInput == "" ? false : true;
int PARRENT_TO_CHILD[2];
int CHILD_TO_PARRENT[2];
if(pipe(CHILD_TO_PARRENT) < 0)
perror("pipe error");
if(validInput)
{
if(pipe(PARRENT_TO_CHILD) < 0)
perror("pipe error");
char* temp = stringCharConvertor(paInput);
write(PARRENT_TO_CHILD[1], temp, strlen(temp));
close(PARRENT_TO_CHILD[1]);
}
pid_t PID = fork();
if(PID > 0)
{
int s;
char buffer[BUFFER_SIZE+1];
memset(buffer, '\0', sizeof(buffer));
close[CHILD_TO_PARRENT[1]];
wait(&s);
if(read(CHILD_TO_PARRENT[0], buffer, BUFFER_SIZE) < 0)
printf("error ");
close(CHILD_TO_PARRENT[0]);
paOutput = buffer;
if(validInput)
close(PARRENT_TO_CHILD[0]);
cout << "\n"+paInput;
}
else
if(PID == 0)
{
dup2(CHILD_TO_PARRENT[1], STDOUT_FILENO);
close(CHILD_TO_PARRENT[1]);
close(CHILD_TO_PARRENT[0]);
if(validInput)
{
dup2(PARRENT_TO_CHILD[0], STDIN_FILENO);
close(PARRENT_TO_CHILD[0]);
close(PARRENT_TO_CHILD[1]);
}
if(execvp(arg[0], arg) < 0)
close(CHILD_TO_PARRENT[1]);
}
}
int main()
{
string input = "one:two:three:four:five:six:seven:eight:nine:ten";
string output = "";
executeCommand(argCut, output, input);
cout << "\n INPUT: "+input <<endl;
cout << "\n OUTPUT: "+output <<endl;
return 0;
}

Answer 1

you should try to replace
char *argCut[] = { "cut", "-d':'", "-f5", (char *)0};
by
char *argCut[] = { "cut", "-d:", "-f5", (char *)0};
no need for quotes
here's some rationale:
running strace on your code shows:
[pid 7641] execve("/usr/bin/cut", ["cut", "-d':'", "-f5"], [/* 85 vars */]) = 0
which is more or less equivalent to the call
/bin/cut "-d':'" "-f5"
which gives the same error
In fact the shell does remove the extra quotes as you may see:
$ echo one:two:three:four:five | strace -f /bin/cut -d':' -f5
execve("/bin/cut", ["/bin/cut", "-d:", "-f5"], [/* 85 vars */]) = 0
=> success
whereas:
$ echo one:two:three:four:five | strace -f /bin/cut "-d':'" -f5
execve("/bin/cut", ["/bin/cut", "-d':'", "-f5"], [/* 85 vars */]) = 0
=> failure