integer extraction from string

Question

I have an input argument string const char* s I know that it starts the sequence of chars which are integers representation ,this sequence could be of any length ,

Answer 1

Try atoi() or the complete strtol():

int x = atoi("23meeting");
int x = (int)strtol("23meeting", (char **)NULL, 10);

Check the man pages on your system (section 3 in Unix).