system調用cmd，怎麽捕捉錯誤msg

#include <stdlib.h>

#include <err.h>

#define BUF 256

int

main (int argc, char *argv[])

{

FILE *fp;

char buf[BUF];

int flag = 0;

//char *cmdline = "/bin/ls -luasx /bin";

char *cmdline = "busybox ftpget -u sgq1 -p sgq123 10.41.181.207 chin.c chin.c";

if ( (fp=popen(cmdline,"r")) ==NULL) {

err(EXIT_FAILURE, "%s", cmdline);

}

while(fgets(buf, BUF, fp) != NULL) {

(void) fputs(buf, stdout);

flag = 1;

}

(void) pclose(fp);

exit (EXIT_SUCCESS);

}