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C - Getting a string from an int

I have a list of all strings of a given length in the format

e.g. length 3

000
100
200
.
.
900
A00
B00
.
.
Z00
a00
b00
.
.
z00
010
.
.
.
zzz

I am trying to write valueof(int pos, int len)

that takes an int position as a parameter and prints the string at that position (for example, valueof(1,3)

prints 000

and valueof(109,3)

printsk10

This is what I tried and it doesn't work:

void valueof(int pos,int len)
{   

    int i=0;
    char arry[62] = {'0','1','2','3','4','5','6','7','8','9',
        'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z',
        'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'};
    char * string = malloc(sizeof(char)*(len+1));
    for(i=0; i<len; i++)
    {
        string[i]='0';
    }
    string[len]='\0';
    i=0;
    while(pos >= 62)
    {
        string[i]=arry[(pos%62)-1];
        i++;
        pos/=62;
    }
    string[i]=arry[pos];

    printf("%s\n",string);
}
+3


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2 answers


So, it pos % 62

returns a number between [0, 61]

. So when you do (pos%62)-1

, you get a number in between [-1, 60]

. Chances are you don't want this.

You should probably rewrite this line:

string[i]=arry[(pos%62)-1];


as:

string[i] = arry[pos % 62];
+5


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Here is the test harness. I would add some bounds checks to the input, otherwise you can intercept the array.

    #include <stdio.h>
    #include <stdlib.h>

    void valueof(int pos,int len)
...

   int main (int argc, char **argv) {
     valueof(atoi(argv[1]), atoi(argv[2]));
   }


To compile gcc vo.c -o vo

./vo 1 3
000
./vo 109 3
k10
+2


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