I need some help with a c programming function. The function is suppose to read in a octal number by string,

Question

and then convert the string to an integer using atoi. If possible please include a simple example. Thanks.

Answer 1

atoi() doesn't support octal numbers, at least not in standard C. strtol() does support it:

#include <stdlib.h>

...

long int number = strtol(theString, NULL, 8);

...

will return the long int value of an octal number in theString.

If you're reading the string from the console, you can make scanf() interpret the input as octal for you:

#include <stdio.h>

...

unsigned int num;

...

scanf("%o", &num);

...

The only use of the atoi function I could think of is if you'd process each digit individually:

#include <stdlib.h>

int readOct(char *theString) {

int num = 0;

int i=0;

char digit[2]=" ";



// each digit

while(theString[i] != '\0') {

// higher octal place value for previous digits

num *= 8;

// add current digit

digit[0] = theString[i];

num += atoi(digit);

i++;

}



return num;

}

But then it would be easier to make use of the fact, that C represents characters as numbers:

int readOct2(char *theString) {

int num = 0;

int i=0;



// each digit

while(theString[i] != '\0') {

num *= 8;

num += theString[i] - '0';

i++;

}



return num;

}