How to extract numbers from string in c? - c

Question

Say I have a string like ab234cid*(s349*(20kd and I want to extract all the numbers 234, 349, 20, what should I do ?

Answer 1

You can do it with strtol, like this:
char *str = "ab234cid*(s349*(20kd", *p = str;
while (*p) { // While there are more characters to process...
if ( isdigit(*p) || ( (*p=='-'||*p=='+') && isdigit(*(p+1)) )) {
// Found a number
long val = strtol(p, &p, 10); // Read number
printf("%ld\n", val); // and print it.
} else {
// Otherwise, move on to the next character.
p++;
}
}
Link to ideone.

Answer 2

A possible solution using sscanf() and scan sets:
const char* s = "ab234cid*(s349*(20kd";
int i1, i2, i3;
if (3 == sscanf(s,
"%*[^0123456789]%d%*[^0123456789]%d%*[^0123456789]%d",
&i1,
&i2,
&i3))
{
printf("%d %d %d\n", i1, i2, i3);
}
where %*[^0123456789] means ignore input until a digit is found. See demo at http://ideone.com/2hB4UW .
Or, if the number of numbers is unknown you can use %n specifier to record the last position read in the buffer:
const char* s = "ab234cid*(s349*(20kd";
int total_n = 0;
int n;
int i;
while (1 == sscanf(s + total_n, "%*[^0123456789]%d%n", &i, &n))
{
total_n += n;
printf("%d\n", i);
}

Answer 3

here after a simple solution using sscanf:
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
char str[256]="ab234cid*(s349*(20kd";
char tmp[256];
int main()
{
int x;
tmp[0]='\0';
while (sscanf(str,"%[^0123456789]%s",tmp,str)>1||sscanf(str,"%d%s",&x,str))
{
if (tmp[0]=='\0')
{
printf("%d\r\n",x);
}
tmp[0]='\0';
}
}

Answer 4

Make a state machine that operates on one basic principle: is the current character a number.
When transitioning from non-digit to digit, you initialize your current_number := number.
when transitioning from digit to digit, you "shift" the new digit in:
current_number := current_number * 10 + number;
when transitioning from digit to non-digit, you output the current_number
when from non-digit to non-digit, you do nothing.
Optimizations are possible.

Answer 5

If the numbers are seprated by whitespace in the string then you can use sscanf(). Since, it's not the case with your example,
you have to do it yourself:
char tmp[256];
for(i=0;str[i];i++)
{
j=0;
while(str[i]>='0' && str[i]<='9')
{
tmp[j]=str[i];
i++;
j++;
}
tmp[j]=0;
printf("%ld", strtol(tmp, &tmp, 10));
// Or store in an integer array
}

Answer 6

#include<stdio.h>
#include<ctype.h>
#include<stdlib.h>
void main(int argc,char *argv[])
{
char *str ="ab234cid*(s349*(20kd", *ptr = str;
while (*ptr) { // While there are more characters to process...
if ( isdigit(*ptr) ) {
// Found a number
int val = (int)strtol(ptr,&ptr, 10); // Read number
printf("%d\n", val); // and print it.
} else {
// Otherwise, move on to the next character.
ptr++;
}
}
}

Answer 7

Or you can make a simple function like this:
// Provided 'c' is only a numeric character
int parseInt (char c) {
return c - '0';
}