In addition to strtok which was already mentioned, your platform may provide a
regcomp function for regular expressions:
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <regex.h>
int main(void)
{
char *header = "This is a sample header\nNumber: 12345\nThis is ano
+ther line\n";
char *number = NULL;
regex_t re;
regmatch_t pmatch[2];
int retval;
regcomp(&re, "^Number: (.+)", REG_EXTENDED | REG_NEWLINE);
retval = regexec(&re, header, sizeof(pmatch)/sizeof(*pmatch), pmatc
+h, 0);
if(retval == 0 && pmatch[1].rm_so != -1)
{
size_t len = pmatch[1].rm_eo - pmatch[1].rm_so;
number = malloc(len + 1);
memcpy(number, header + pmatch[1].rm_so, len);
number[len] = '\0';
printf("Number is %s\n", number);
}
else
{
printf("Match failed\n");
}
regfree(&re);
free(number);
return 0;
}
No error checking is done and number is stored as a string, atoi()/strtol() family can turn it into an integer.