I am trying to find out if there is an alternative way of converting string to integer in C.
I regularly pattern the following in my code.
char s[] =
Robust C89 strtol
-based solution
With:
atoi
family)strtol
(e.g. no leading whitespace nor trailing trash chars)#include <assert.h>
#include <ctype.h>
#include <errno.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
typedef enum {
STR2INT_SUCCESS,
STR2INT_OVERFLOW,
STR2INT_UNDERFLOW,
STR2INT_INCONVERTIBLE
} str2int_errno;
/* Convert string s to int out.
*
* @param[out] out The converted int. Cannot be NULL.
*
* @param[in] s Input string to be converted.
*
* The format is the same as strtol,
* except that the following are inconvertible:
*
* - empty string
* - leading whitespace
* - any trailing characters that are not part of the number
*
* Cannot be NULL.
*
* @param[in] base Base to interpret string in. Same range as strtol (2 to 36).
*
* @return Indicates if the operation succeeded, or why it failed.
*/
str2int_errno str2int(int *out, char *s, int base) {
char *end;
if (s[0] == '\0' || isspace(s[0]))
return STR2INT_INCONVERTIBLE;
errno = 0;
long l = strtol(s, &end, base);
/* Both checks are needed because INT_MAX == LONG_MAX is possible. */
if (l > INT_MAX || (errno == ERANGE && l == LONG_MAX))
return STR2INT_OVERFLOW;
if (l < INT_MIN || (errno == ERANGE && l == LONG_MIN))
return STR2INT_UNDERFLOW;
if (*end != '\0')
return STR2INT_INCONVERTIBLE;
*out = l;
return STR2INT_SUCCESS;
}
int main(void) {
int i;
/* Lazy to calculate this size properly. */
char s[256];
/* Simple case. */
assert(str2int(&i, "11", 10) == STR2INT_SUCCESS);
assert(i == 11);
/* Negative number . */
assert(str2int(&i, "-11", 10) == STR2INT_SUCCESS);
assert(i == -11);
/* Different base. */
assert(str2int(&i, "11", 16) == STR2INT_SUCCESS);
assert(i == 17);
/* 0 */
assert(str2int(&i, "0", 10) == STR2INT_SUCCESS);
assert(i == 0);
/* INT_MAX. */
sprintf(s, "%d", INT_MAX);
assert(str2int(&i, s, 10) == STR2INT_SUCCESS);
assert(i == INT_MAX);
/* INT_MIN. */
sprintf(s, "%d", INT_MIN);
assert(str2int(&i, s, 10) == STR2INT_SUCCESS);
assert(i == INT_MIN);
/* Leading and trailing space. */
assert(str2int(&i, " 1", 10) == STR2INT_INCONVERTIBLE);
assert(str2int(&i, "1 ", 10) == STR2INT_INCONVERTIBLE);
/* Trash characters. */
assert(str2int(&i, "a10", 10) == STR2INT_INCONVERTIBLE);
assert(str2int(&i, "10a", 10) == STR2INT_INCONVERTIBLE);
/* int overflow.
*
* `if` needed to avoid undefined behaviour
* on `INT_MAX + 1` if INT_MAX == LONG_MAX.
*/
if (INT_MAX < LONG_MAX) {
sprintf(s, "%ld", (long int)INT_MAX + 1L);
assert(str2int(&i, s, 10) == STR2INT_OVERFLOW);
}
/* int underflow */
if (LONG_MIN < INT_MIN) {
sprintf(s, "%ld", (long int)INT_MIN - 1L);
assert(str2int(&i, s, 10) == STR2INT_UNDERFLOW);
}
/* long overflow */
sprintf(s, "%ld0", LONG_MAX);
assert(str2int(&i, s, 10) == STR2INT_OVERFLOW);
/* long underflow */
sprintf(s, "%ld0", LONG_MIN);
assert(str2int(&i, s, 10) == STR2INT_UNDERFLOW);
return EXIT_SUCCESS;
}
GitHub upstream.
Based on: https://stackoverflow.com/a/6154614/895245
You can always roll your own!
#include <stdio.h>
#include <string.h>
#include <math.h>
int my_atoi(const char* snum)
{
int idx, strIdx = 0, accum = 0, numIsNeg = 0;
const unsigned int NUMLEN = (int)strlen(snum);
/* Check if negative number and flag it. */
if(snum[0] == 0x2d)
numIsNeg = 1;
for(idx = NUMLEN - 1; idx >= 0; idx--)
{
/* Only process numbers from 0 through 9. */
if(snum[strIdx] >= 0x30 && snum[strIdx] <= 0x39)
accum += (snum[strIdx] - 0x30) * pow(10, idx);
strIdx++;
}
/* Check flag to see if originally passed -ve number and convert result if so. */
if(!numIsNeg)
return accum;
else
return accum * -1;
}
int main()
{
/* Tests... */
printf("Returned number is: %d\n", my_atoi("34574"));
printf("Returned number is: %d\n", my_atoi("-23"));
return 0;
}
This will do what you want without clutter.
Ok, I had the same problem.I came up with this solution.It worked for me the best.I did try atoi() but didn't work well for me.So here is my solution:
void splitInput(int arr[], int sizeArr, char num[])
{
for(int i = 0; i < sizeArr; i++)
// We are subtracting 48 because the numbers in ASCII starts at 48.
arr[i] = (int)num[i] - 48;
}
Just wanted to share a solution for unsigned long aswell.
unsigned long ToUInt(char* str)
{
unsigned long mult = 1;
unsigned long re = 0;
int len = strlen(str);
for(int i = len -1 ; i >= 0 ; i--)
{
re = re + ((int)str[i] -48)*mult;
mult = mult*10;
}
return re;
}
In C++, you can use a such function:
template <typename T>
T to(const std::string & s)
{
std::istringstream stm(s);
T result;
stm >> result;
if(stm.tellg() != s.size())
throw error;
return result;
}
This can help you to convert any string to any type such as float, int, double...
This function will help you
int strtoint_n(char* str, int n)
{
int sign = 1;
int place = 1;
int ret = 0;
int i;
for (i = n-1; i >= 0; i--, place *= 10)
{
int c = str[i];
switch (c)
{
case '-':
if (i == 0) sign = -1;
else return -1;
break;
default:
if (c >= '0' && c <= '9') ret += (c - '0') * place;
else return -1;
}
}
return sign * ret;
}
int strtoint(char* str)
{
char* temp = str;
int n = 0;
while (*temp != '\0')
{
n++;
temp++;
}
return strtoint_n(str, n);
}
Ref: http://amscata.blogspot.com/2013/09/strnumstr-version-2.html