Where to find resource on "how to analyze " system call output
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I like to bypass some of the Bluetooth "resources" in my C / C++ code by using (direct) system calls. I can czech for return value, but like to analyze more of the output, in including errors. Where do I start ? Contrary to my opinion ( about RTFM ) - can somebody give me link to "RTFM" how to do it ?
system(" hcitool dev");
return to stdout (?)
Devices:
hci1 00:50:B6:80:4D:5D
hci0 00:15:83:15:A2:CB -
I like to bypass some of the Bluetooth "resources" in my C / C++ code by using (direct) system calls. I can czech for return value, but like to analyze more of the output, in including errors. Where do I start ? Contrary to my opinion ( about RTFM ) - can somebody give me link to "RTFM" how to do it ?
system(" hcitool dev");
return to stdout (?)
Devices:
hci1 00:50:B6:80:4D:5D
hci0 00:15:83:15:A2:CBRather than system(), you want to use popen(). The only problem is that popen() doesn't supply a separate FILE for stderr, so you have to use output redirection to capture both e.g.
FILE *cmd = popen("hcitool dev 2>&1", "r");
char *buffer = NULL;
size_t len = 0;
ssize_t readlen;
while ( (readlen = getline(&buffer, len, cmd)) > 0)
{
/* process input buffer */
}
free(buffer);
pclose(cmd);You could perhaps also use output redirection to capture output separately e.g.
FILE *cmd = popen("hcitool dev 2>/tmp/hcierrs", "r");
/* process input as above */
FILE *cmd_errs = fopen("/tmp/hcierrs", "r");
/* loop through input from cmd_errs ... */
unlink("/tmp/hcierrs");If you're going to do that, you might want to look at creating unique temporary file names, so that you don't clobber output if you happen to have more than one instance of the program running at the same time.
mkstemp()can help you here. For the really advanced, you might look into trying "roll your own" version of popen that usesfork()and one of theexec()functions to separate out stdout and stderr to two separate FILES.Keep Calm and Carry On
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Rather than system(), you want to use popen(). The only problem is that popen() doesn't supply a separate FILE for stderr, so you have to use output redirection to capture both e.g.
FILE *cmd = popen("hcitool dev 2>&1", "r");
char *buffer = NULL;
size_t len = 0;
ssize_t readlen;
while ( (readlen = getline(&buffer, len, cmd)) > 0)
{
/* process input buffer */
}
free(buffer);
pclose(cmd);You could perhaps also use output redirection to capture output separately e.g.
FILE *cmd = popen("hcitool dev 2>/tmp/hcierrs", "r");
/* process input as above */
FILE *cmd_errs = fopen("/tmp/hcierrs", "r");
/* loop through input from cmd_errs ... */
unlink("/tmp/hcierrs");If you're going to do that, you might want to look at creating unique temporary file names, so that you don't clobber output if you happen to have more than one instance of the program running at the same time.
mkstemp()can help you here. For the really advanced, you might look into trying "roll your own" version of popen that usesfork()and one of theexec()functions to separate out stdout and stderr to two separate FILES.Keep Calm and Carry On
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