strtol - Convert the number from string into interger
NAME
- strtol, strtoll, strtoq - convert a string to a long integer
SYNOPSIS
#include <stdlib.h>
long int strtol(const char *nptr, char **endptr, int base);
long long int strtoll(const char *nptr, char **endptr, int base);
strtoll():
_ISOC99_SOURCE
|| /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
long int strtol(const char *nptr, char **endptr, int base);
long long int strtoll(const char *nptr, char **endptr, int base);
strtoll():
_ISOC99_SOURCE
|| /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
DESCRIPTION
- The strtol() function converts the initial part of the string in nptr to a long integer value according to the given base.
- If base is 2 then binary, if 8 then octal, if 10 then decimal & 16 for hexa decimal.
- In bases above 10, the letter 'A' in either uppercase or lowercase represents 10, 'B' represents 11, and so forth, with 'Z' representing 35.
- Checked in sample program, Hence If u give base as 20 then, f as 15, g as 16, h as 17... j as 19, k will throw an error.
- If endptr is not NULL, strtol() stores the address of the first invalid character in *endptr.
- If there were no digits at all, strtol() stores the original value of nptr in *endptr (and returns 0).
RETURN VALUE
- The strtol() function returns the result of the conversion, unless the value would underflow or overflow.
- If an underflow occurs, strtol() returns LONG_MIN.
- If an overflow occurs, strtol() returns LONG_MAX.
- In both cases, errno is set to ERANGE.
Note: Program should set errno to 0 before the call, after call check the errno.
Difference between atoi, strtol & sscanf :
atoi()Pro: Simple.
Pro: Convert to an int.
Pro: In the C standard library.
Pro: Fast.
Con: No error handling.
Con: Handle neither hexadecimal nor octal.
atol()
Pro: Simple.
Pro: In the C standard library.
Pro: Fast.
Con: Converts to an long, not int which may differ in size.
Con: No error handling.
Con: Handle neither hexadecimal nor octal.
strtol()
Pro: Simple.
Pro: In the C standard library.
Pro: Good error handling.
Pro: Fast.
Con: Convert to an long, not int which may differ in size.
strtoul()
Pro: Simple.
Pro: In the C standard library.
Pro: Good error handling.
Pro: Fast.
---: Appears to not complain about negative numbers.
Con: Converts to an unsigned long, not int which may differ in size.
sscanf(..., "%i", ...)
Pro: In the C standard library.
Pro: Converts to int.
---: Middle-of-the-road complexity.
Con: Slow.
Con: OK error handling (overflow is not defined).
#define BASE_DECIMAL 10
Eg: pid_count = (int)strtol(buf, NULL, BASE_DECIMAL);
Program:
/* strtol - convert str to interger by Velraj.K
* Check : http://velrajcoding.blogspot.in
*/
#include <stdio.h>>
#include <errno.h> // errno & ERANGE
#include <stdlib.h> // strtol & LONG_MAX
#include <limits.h> // LONG_MAX & LONG_MIN
#include <string.h> // for strerror
enum {
FAILED = -1,
SUCCESS,
};
/*************************************************************************************
* FUNCTION NAME: convert_str_to_int
*
* DESCRIPTION : convert the string into interget value
*
* RETURNS : None
* RETURNS : FAIL on failure,
* SUCCESS on successfull update.
*************************************************************************************/
static int convert_str_to_int(char *str_val, unsigned int *conv_value, char **save_endptr)
{
char *endptr = NULL;
long int result = 0;
if (!str_val || !conv_value) {
printf("input string is NULL \n");
return FAILED;
}
errno = 0;
result = strtol(str_val, &endptr, 10);
*conv_value = (unsigned int)result;
if (((errno == ERANGE) && ((result == LONG_MAX) || (result == LONG_MIN))) ||
((errno != 0) && (result == 0))) {
printf("Error: conversion %s(%d) \n", strerror(errno), errno);
return FAILED;
}
/* Save the endptr string for any future usage, after conversion. */
if (save_endptr) {
*save_endptr = endptr;
if ((*save_endptr) && (**save_endptr != '\0') &&
(!isspace(**save_endptr))) {
printf("End string of input value saved as:%s \n", *save_endptr);
}
}
if (endptr == str_val) {
printf("No digits were found \n");
return FAILED;
}
return SUCCESS;
}
int main()
{
int value = 0;
char *endptr = NULL;
char str[32] = {0};
while (1) {
printf("Enter the number to convert strint to int : ");
// scanf("%[^\t\n]s", str);
fgets(str, sizeof(str), stdin);
convert_str_to_int(str, &value, &endptr);
/*
* Check the endptr has any invalid trailing strings,
* after strtol conversion.
*/
if ((endptr) && (*endptr != '\0') && (!isspace(*endptr))) {
printf("Error invalid string is present \n");
} else {
printf("Input value : %s", str);
printf("Value after convert val to : %d\n",value);
}
}
convert_str_to_int("5m", &value, &endptr);
if ((endptr) && (*endptr != '\0') && (!isspace(*endptr))) {
printf("Error invalid string is present for 5m \n");
} else {
printf("Value after conver 5m val : %d \n", value);
}
return 0;
}
Output:
velraj@virtual-machine:~/velrajk/sample$ ./a.outEnter the number to convert strint to int : 5
Input value : 5
Value after convert val to : 5
Enter the number to convert strint to int : 5m
End string of input value saved as:m
Error invalid string is present
Enter the number to convert strint to int : 5
Input value : 5
Value after convert val to : 5
Enter the number to convert strint to int : 5 m
Input value : 5 m
Value after convert val to : 5
Enter the number to convert strint to int : 5 mnews
Input value : 5 mnews
Value after convert val to : 5
Enter the number to convert strint to int : ^C
