C++ Fork child, ask child for process list, kill a process in Linux -


i'm trying create child process, send child process command "listall". child process should issue system command ps , return list parent process. parent process should choose process , kill it. have far i'm having trouble getting run.

#include <stdio.h> #include <unistd.h> #include <cstring> #include <stdlib.h> #include <iostream> #include <sys/wait.h>  char* getlistofprocesses(const char* cmd)  {     file* pipe = popen(cmd, "r");     if (!pipe) return (char*)"error";     char buffer[128];     char *result = new char[1024];     while(!feof(pipe)) {         if(fgets(buffer, 128, pipe) != null)             strcat(result, buffer);     }     pclose(pipe);     return result; }  int spawngedit() {     pid_t gpid = fork();     if(gpid == 0)     {         execl("gedit", "gedit", null);         exit(-1);     }     else     {     }     return 0; }  int main(int argc, char **argv) {        int p2c[2];     int c2p[2];     pipe(p2c);     pipe(c2p);     pid_t cpid = fork();     char cmd[50];     char* listofprocesses = new char[1024];     spawngedit();      if (cpid == 0)     {         close(p2c[1]);          close(c2p[0]);          read(p2c[0], cmd, 10);         if(strcmp(cmd,"listall") == 0)         {             write(c2p[1], getlistofprocesses("ps"), 1024);             close(p2c[0]);             close(c2p[1]);         }     }     else if (cpid > 0)     {         close(c2p[1]);          close(p2c[0]);          write(p2c[1], "listall", 10);         wait(null);         read(c2p[0], listofprocesses,1024);         printf("%s",listofprocesses);          //todo         //get user input of pid         //kill pid         close(c2p[0]);         close(p2c[1]);     }     else     {         // fork failed         printf("forking failed!\n");         exit(1);     }     return 0; }

these errors i'm getting when try compile it:

/tmp/ccitpioz.o: in function `getlistofprocesses(char const*)': test.cpp:(.text+0x53): undefined reference `operator new[](unsigned long)' /tmp/ccitpioz.o: in function `main': test.cpp:(.text+0x166): undefined reference `operator new[](unsigned long)' /tmp/ccitpioz.o: in function `__static_initialization_and_destruction_0(int, int)': test.cpp:(.text+0x2c0): undefined reference `std::ios_base::init::init()' test.cpp:(.text+0x2cf): undefined reference `std::ios_base::init::~init()' collect2: error: ld returned 1 exit status

i'm compiling with: 

cc test.cpp -o test

compilation errors occurred on line number:9,53,64 can solved using these:

line 9: file* pipe = popen(cmd.data(), "r");

line 53: write(c2p[1], getlistofprocesses("ps").data(), 1024);

line 64: printf("%s",listofprocesses.data());

reason: these popen,write,printf requires char* arguments passing them std::string. have use std::string.data() function instead returns pointer character array represented std::string object.

and error on line 63, refer this.

ps:- edits in question:

line 10: if (!pipe) return (char*)"error";

line 12: char *result = new char[1024];

line 53: (change in line 7) char* getlistofprocesses(const char* cmd)

a bit of advice: use wait(null); in parent process before reading listofprocesses , exit(0); @ end of child process.

working code:

#include <stdio.h> #include <unistd.h> #include <cstring> #include <stdlib.h> #include <iostream> #include <sys/wait.h>  char* getlistofprocesses(const char* cmd)  {     file* pipe = popen(cmd, "r");     if (!pipe) return (char*)"error";     char buffer[128];     char *result = new char[1024];     while(!feof(pipe)) {         if(fgets(buffer, 128, pipe) != null)             strcat(result, buffer);     }     pclose(pipe);     return result; }  int spawngedit() {     pid_t gpid = fork();     if(gpid == 0)     {         execl("gedit", "gedit", null);         exit(-1);     }     else     {     }     return 0; }  int main(int argc, char **argv) {        int p2c[2];     int c2p[2];     pipe(p2c);     pipe(c2p);     pid_t cpid = fork();     char cmd[50];     char* listofprocesses = new char[1024];     spawngedit();      if (cpid == 0)     {         close(p2c[1]);          close(c2p[0]);          read(p2c[0], cmd, 10);         if(strcmp(cmd,"listall") == 0)         {             write(c2p[1], getlistofprocesses("ps"), 1024);             close(p2c[0]);             close(c2p[1]);         }         exit(0);     }     else if (cpid > 0)     {         close(c2p[1]);          close(p2c[0]);          write(p2c[1], "listall", 10);         wait(null);         read(c2p[0], listofprocesses,1024);         printf("%s",listofprocesses);          //todo         //get user input of pid         //kill pid         close(c2p[0]);         close(p2c[1]);     }     else     {         // fork failed         printf("forking failed!\n");         exit(1);     }     return 0; }

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