How to extract some formatted string from the buffer using scanf? - c

Question

I need to extract both "rudolf" and "12" from that long string: "hello, i know that rudolph=12 but it so small..." using scanf, how can I do it?
This buffer can contains any formatted strings like ruby=45 or bomb=1, and I dont know it in advance.
I am trying something like that, but it was unsuccessful
#include <stdio.h>
int main()
{
char sentence[] = "hello, i know that rudolph=12 but it so small...";
char name[32];
int value;
sscanf(sentence, "%[a-z]=%d", name, &value);
printf("%s -> %d\n", name, value);
getchar();
return 0;
}

Answer 1

Iterate through the sentence using a temporary pointer and %n to extract each sub-string.
%n will give the number of characters processed by the scan to that point. Add that to the temporary pointer to advance through the sentence.
Try to parse from each sub-string the name and value. The scanset %31[^=] will scan a maximum of 31 characters, leaving room in name for a terminating zero. It will scan all characters that are not an =. Then the format string will scan the = and try to scan an integer.
#include <stdio.h>
#include <stdlib.h>
int main (void) {
char sentence[] = "hello, i know that rudolph=12 but it so small...";
char string[sizeof sentence] = "";
char name[32] = "";
char *temp = sentence;
int value = 0;
int count = 0;
int parsed = 0;
while (1 == sscanf(temp, "%s%n", string, &count)) {
temp += count;
if (2 == sscanf(string, "%31[^=]=%d", name, &value)) {
parsed = 1;
break;
}
}
if (parsed) {
printf("%s %d\n", name, value);
}
return 0;
}

Answer 2

You can write your own string serach engine. Which could be quite simple, let's for example:
advance until you find one of [a-z]
remember position
advance until the end of [a-z]
check if it's = now
if it is, there was our variable name
advance until end of value
return it
if there's no =, omit everything that is not a [a-z] ie. can't be variable name
A sample program:
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
struct find_assignment_s {
const char *line;
const char *var;
size_t varlen;
const char *val;
size_t vallen;
};
struct find_assignment_s find_assignment_init(const char *line) {
return (struct find_assignment_s){.line = line};
}
int find_assignment(struct find_assignment_s *t) {
while (*t->line) {
const char *p = t->line;
while (*p && isalpha((unsigned char)*p)) p++;
// There is at least one alphabetic character and there is a space right after.
if (t->line != p && *p == '=') {
// Found a "variable="!
t->var = t->line;
t->varlen = p - t->line;
// value is up until a space is found
t->val = p + 1;
while (*p && !isspace((unsigned char)*p)) p++;
t->vallen = p - t->val;
// Advance the pointer behind value.
t->line = *p ? p + 1 : p;
return 1;
}
// Ignore spaces
while (*p && !isalpha((unsigned char)*p)) p++;
// Advance over whole word.
t->line = p;
}
return 0;
}
int main() {
const char line[] = "hello, i know that rudolph=12 but it so small... a=b c=d fdnajn=123";
for (struct find_assignment_s fs = find_assignment_init(line);
find_assignment(&fs) == 1; ) {
printf("%.*s = %.*s\n", (int)fs.varlen, fs.var, (int)fs.vallen, fs.val);
}
}
outputs:
rudolph = 12
a = b
c = d
fdnajn = 123