C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Passing Variables To System()          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message JLK Guest Posted: Wed Jun 30, 2004 12:49 am    Post subject: Passing Variables To System() I'm having a bit of a time with the following code. I can script this real easy in Bash but I'm trying to practice my C++: ******************************************************* #include <iostream> #include <string> using namespace std; int main () { string user = "fred"; string cmd; cmd = "curl -d userid=" + user + "&press=submit http://URL"; cout << "command = " << cmd << endl; cout << "command = " << cmd.c_str() << endl; system(cmd.c_str()); return 0; } ******************************************************* If you run it you'll notice that both of the couts will produce the full line ok. However, if I try to pass either one to system() it will fail as nothing past "curl -d userid=" gets appended. How can you pass variables such as parameters to system() ?? Back to top Leor Zolman Guest Posted: Wed Jun 30, 2004 1:00 am    Post subject: Re: Passing Variables To System() On 29 Jun 2004 17:49:59 -0700, [email]jonkokko (AT) gmail (DOT) com[/email] (JLK) wrote: Quote: I'm having a bit of a time with the following code. I can script this real easy in Bash but I'm trying to practice my C++: ******************************************************* #include #include using namespace std; int main () { string user = "fred"; string cmd; cmd = "curl -d userid=" + user + "&press=submit http://URL"; cout << "command = " << cmd << endl; cout << "command = " << cmd.c_str() << endl; system(cmd.c_str()); return 0; } ******************************************************* If you run it you'll notice that both of the couts will produce the full line ok. However, if I try to pass either one to system() it will fail as nothing past "curl -d userid=" gets appended. How can you pass variables such as parameters to system() ?? Depending upon what operating system you're running under (and it sounds like yours is some flavor of Unix), the '&' character is going to have different meanings to the command processor/shell. I happen to be testing under Windows XP and running 4NT as my command processor; the '&' is an "end of command" separator just like ';' is under the Unix shells. On your machine, wouldn't '&' mean "run the previous command in the background" ? And the remainder would be interpreted as setting an environment variable named 'press' to the value 'submit', with the 'http' being then seen as the start of yet another command? I'd reocommend stragetic placement of some backslashes, for starters... -leor -- Leor Zolman --- BD Software --- www.bdsoft.com On-Site Training in C/C++, Java, Perl and Unix C++ users: download BD Software's free STL Error Message Decryptor at: www.bdsoft.com/tools/stlfilt.html Back to top JLK Guest Posted: Wed Jun 30, 2004 7:55 am    Post subject: Re: Passing Variables To System() Leor Zolman <leor (AT) bdsoft (DOT) com> wrote Quote: On 29 Jun 2004 17:49:59 -0700, [email]jonkokko (AT) gmail (DOT) com[/email] (JLK) wrote: I'm having a bit of a time with the following code. I can script this real easy in Bash but I'm trying to practice my C++: ******************************************************* #include #include using namespace std; int main () { string user = "fred"; string cmd; cmd = "curl -d userid=" + user + "&press=submit http://URL"; cout << "command = " << cmd << endl; cout << "command = " << cmd.c_str() << endl; system(cmd.c_str()); return 0; } ******************************************************* If you run it you'll notice that both of the couts will produce the full line ok. However, if I try to pass either one to system() it will fail as nothing past "curl -d userid=" gets appended. How can you pass variables such as parameters to system() ?? Depending upon what operating system you're running under (and it sounds like yours is some flavor of Unix), the '&' character is going to have different meanings to the command processor/shell. I happen to be testing under Windows XP and running 4NT as my command processor; the '&' is an "end of command" separator just like ';' is under the Unix shells. On your machine, wouldn't '&' mean "run the previous command in the background" ? And the remainder would be interpreted as setting an environment variable named 'press' to the value 'submit', with the 'http' being then seen as the start of yet another command? I'd reocommend stragetic placement of some backslashes, for starters... -leor You are correct as I'm running linux and the & symbol is a 'background' command. However, that is only true if the character stands alone at the end of a command (such as: script.sh &) If it gets correctly appended and runs as "curl -d userid=user&press=submit http://URL" then it would be ok. It appears my variable insert is not getting appended along with the other half of the script. The weird part is that if I hard code USER I can run everything OK. I'm only bombing out when I try to insert it as a variable. Back to top John Harrison Guest Posted: Wed Jun 30, 2004 8:39 am    Post subject: Re: Passing Variables To System() "JLK" <jonkokko (AT) gmail (DOT) com> wrote Quote: Leor Zolman <leor (AT) bdsoft (DOT) com> wrote On 29 Jun 2004 17:49:59 -0700, [email]jonkokko (AT) gmail (DOT) com[/email] (JLK) wrote: I'm having a bit of a time with the following code. I can script this real easy in Bash but I'm trying to practice my C++: ******************************************************* #include #include using namespace std; int main () { string user = "fred"; string cmd; cmd = "curl -d userid=" + user + "&press=submit http://URL"; cout << "command = " << cmd << endl; cout << "command = " << cmd.c_str() << endl; system(cmd.c_str()); return 0; } ******************************************************* If you run it you'll notice that both of the couts will produce the full line ok. However, if I try to pass either one to system() it will fail as nothing past "curl -d userid=" gets appended. How can you pass variables such as parameters to system() ?? Depending upon what operating system you're running under (and it sounds like yours is some flavor of Unix), the '&' character is going to have different meanings to the command processor/shell. I happen to be testing under Windows XP and running 4NT as my command processor; the '&' is an "end of command" separator just like ';' is under the Unix shells. On your machine, wouldn't '&' mean "run the previous command in the background" ? And the remainder would be interpreted as setting an environment variable named 'press' to the value 'submit', with the 'http' being then seen as the start of yet another command? I'd reocommend stragetic placement of some backslashes, for starters... -leor You are correct as I'm running linux and the & symbol is a 'background' command. However, that is only true if the character stands alone at the end of a command (such as: script.sh &) If it gets correctly appended and runs as "curl -d userid=user&press=submit http://URL" then it would be ok. It appears my variable insert is not getting appended along with the other half of the script. The weird part is that if I hard code USER I can run everything OK. I'm only bombing out when I try to insert it as a variable. No, something else is going on. Your cmd string is correct, as proved by the previous to cout << statements. By the time your program gets to the system call, it is completely irrelevant whether the cmd string was composed of variables or not, its just a string. What you are saying is that you get different results with two identical strings depending on whether that string was original composed from a variable or not. Frankly, that is impossible, something else is going wrong. john Back to top JLK Guest Posted: Wed Jun 30, 2004 5:34 pm    Post subject: Re: Passing Variables To System() "John Harrison" <john_andronicus (AT) hotmail (DOT) com> wrote Quote: "JLK" <jonkokko (AT) gmail (DOT) com> wrote in message news:f9001473.0406292355.3cb4f638 (AT) posting (DOT) google.com... Leor Zolman <leor (AT) bdsoft (DOT) com> wrote in message news:<ut34e0le99nuj7cg072tcdnk0etrn2md33 (AT) 4ax (DOT) com>... On 29 Jun 2004 17:49:59 -0700, [email]jonkokko (AT) gmail (DOT) com[/email] (JLK) wrote: I'm having a bit of a time with the following code. I can script this real easy in Bash but I'm trying to practice my C++: ******************************************************* #include #include using namespace std; int main () { string user = "fred"; string cmd; cmd = "curl -d userid=" + user + "&press=submit http://URL"; cout << "command = " << cmd << endl; cout << "command = " << cmd.c_str() << endl; system(cmd.c_str()); return 0; } ******************************************************* If you run it you'll notice that both of the couts will produce the full line ok. However, if I try to pass either one to system() it will fail as nothing past "curl -d userid=" gets appended. How can you pass variables such as parameters to system() ?? Depending upon what operating system you're running under (and it sounds like yours is some flavor of Unix), the '&' character is going to have different meanings to the command processor/shell. I happen to be testing under Windows XP and running 4NT as my command processor; the '&' is an "end of command" separator just like ';' is under the Unix shells. On your machine, wouldn't '&' mean "run the previous command in the background" ? And the remainder would be interpreted as setting an environment variable named 'press' to the value 'submit', with the 'http' being then seen as the start of yet another command? I'd reocommend stragetic placement of some backslashes, for starters... -leor You are correct as I'm running linux and the & symbol is a 'background' command. However, that is only true if the character stands alone at the end of a command (such as: script.sh &) If it gets correctly appended and runs as "curl -d userid=user&press=submit http://URL" then it would be ok. It appears my variable insert is not getting appended along with the other half of the script. The weird part is that if I hard code USER I can run everything OK. I'm only bombing out when I try to insert it as a variable. No, something else is going on. Your cmd string is correct, as proved by the previous to cout << statements. By the time your program gets to the system call, it is completely irrelevant whether the cmd string was composed of variables or not, its just a string. What you are saying is that you get different results with two identical strings depending on whether that string was original composed from a variable or not. Frankly, that is impossible, something else is going wrong. john Well, I'm definately open to suggestions. I'm using c++ on a linux box to compile with. I've posted to a couple of other forums as well and am still coming up blank. Back to top red floyd Guest Posted: Wed Jun 30, 2004 8:52 pm    Post subject: Re: Passing Variables To System() JLK wrote: [redacted] Quote: Well, I'm definately open to suggestions. I'm using c++ on a linux box to compile with. I've posted to a couple of other forums as well and am still coming up blank. It *IS* the ampersand. On *nix, system("cmd") invokes $SHELL -c "cmd". The ampersand is interpreted by the shell as the background operator. You need to quote the ampersand either with a backslash, or putting it inside single quotes. Back to top Owen Jacobson Guest Posted: Thu Jul 01, 2004 2:49 am    Post subject: Re: Passing Variables To System() On Wed, 30 Jun 2004 20:52:28 +0000, red floyd wrote: Quote: JLK wrote: [redacted] Well, I'm definately open to suggestions. I'm using c++ on a linux box to compile with. I've posted to a couple of other forums as well and am still coming up blank. It *IS* the ampersand. On *nix, system("cmd") invokes $SHELL -c "cmd". The ampersand is interpreted by the shell as the background operator. You need to quote the ampersand either with a backslash, or putting it inside single quotes. <off-topic bits> And, in case you're firmly convinced that the & is only relevant at the end of a command, consider: [owen@eidolon owen]$ ls | egrep -i '^s' & echo LAST COMMAND IN PARALLEL; [1] 6242 LAST COMMAND IN PARALLEL [owen@eidolon owen]$ Sentret.gif sigbeast.c sigfile-bits.txt SOBAKASU.MP3 spinbottle Splashdown [1]+ Done ls --color=tty | egrep -i '^s' [GNU bash, version 2.05b.0(1)-release (i386-redhat-linux-gnu)] </otb> -- Some say the Wired doesn't have political borders like the real world, but there are far too many nonsense-spouting anarchists or idiots who think that pranks are a revolution. 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