Convert chars from pointer to integer num - c

Question

if the user enter a string,than is save every part of it with strtok, and one of the part was numbers, how i can convert this numbers to integer?
my goal is to get this string : "matrix 3 3 ", and to verify that the user didnt enter double or float, just integer num. I tried to do casting but it is didnt work
thx!

Answer 1

There are different possible ways, but concerning
my goal is [...] to verify that the user didnt enter double or float, just integer num.
you probably aim for full input validation. In that case, you must use strtol().
#include <stdlib.h>
#include <limits.h>
int main(void)
{
const char *str = "42"; // in your code, some result from strtok
char *endptr;
long num = strtol(str, &endptr, 10);
if (endptr == str || *endptr)
{
// not parsed successfully
return 1; // error and out ... do whatever is suitable
}
if (num > INT_MAX || num < INT_MIN)
{
// value was outside int range
return 1;
}
int x = (int)num;
return 0;
}
If you actually want a long, for checking the range, set errno to 0 before calling strtol() and check for errno == ERANGE afterwards. (include errno.h for this)
For the sake of completeness, in response to your comment, of course you can do it all manually, but it's tedious and error prone and less efficient, so I'd never recommend that. See here an example for parsing unsigned integers from strings, with error checking:
#include <stdio.h>
#include <string.h>
// write result to *result, return 0 on error, 1 on success:
int parseuint(unsigned int *result, const char *str)
{
if (!str || !*str) return 0;
size_t len = strlen(str);
unsigned char bcd[len];
for (size_t i = 0; i < len; ++i)
{
if (str[i] < '0' || str[i] > '9') return 0;
bcd[i] = str[i] - '0';
}
size_t scanstart = 0;
*result = 0;
unsigned int mask = 1;
while (scanstart < len)
{
if (!mask) return 0;
if (bcd[len-1] & 1) *result |= mask;
mask <<=1;
for (size_t i = len-1; i > scanstart; --i)
{
bcd[i] >>= 1;
if (bcd[i-1] & 1) bcd[i] |= 8;
}
bcd[scanstart] >>= 1;
while (scanstart < len && !bcd[scanstart]) ++scanstart;
for (size_t i = scanstart; i < len; ++i)
{
if (bcd[i] > 7) bcd[i] -= 3;
}
}
return 1;
}
int main(void)
{
unsigned int a;
if (parseuint(&a, "4258"))
{
printf("parsed: %u\n", a);
}
else
{
puts("error parsing 4258");
}
if (parseuint(&a, "13.7"))
{
printf("parsed: %u\n", a);
}
else
{
puts("error parsing 13.7");
}
if (parseuint(&a, "12345678901234567890"))
{
printf("parsed: %u\n", a);
}
else
{
puts("error parsing 12345678901234567890");
}
}