C Arrays Not Retaining Values - c

Question

I'm writing a simple Base64 decoding function in C. The output of this function looks correct (based on comparing the result with existing tools) when using the printf() debugging lines as below:
unsigned char * b64decode(char *line)
{
char *idx;
unsigned char *decode;
int i,j,len,dlen,hold = 0;
idx = strchr(line, '\n'); //index of newline
len = idx - line; //lenght of string
dlen = 3 * (len / 4); //decoded length
decode = malloc((sizeof(unsigned char) * dlen) + 1);
pad = 0;
for (i = 0; i <= len; i++) { //deindex from ASCII
line[i] = deindex(line[i]);
}
for(i = 0, j = u0; i < len; i++,j++) {
hold |= (line[i] << 18);
hold |= (line[++i] << 12);
hold |= (line[++i] << 6);
hold |= line[++i];
decode[j] = hold >> 16;
printf("%d ", decode[j]);
decode[++j] = (hold >> 8) & 0xFF;
printf("%d ", decode[j]);
decode[++j] = hold & 0xFF;
printf("%d ", decode[j]);
hold = 0;
}
if (pad) //terminate before padding
decode[dlen - pad] = '\0';
return decode;
}
Which produces the (partial) output:
29 66 31 77 11 15 2 31 79 19 78 60 26 105 101 31 73 28 14 78 19 1 11 7
78 27 1 22 69 54 0 30 1 73 100 32 84 29 29 67 51 83 78 101 82 6 0 71 84
28 13 69 77 7 4 12 83 18 60 12 30 8 73 26 9 17 79 20 76 33 26 71 43 0 5
29 71 89 17 4 9 0 100 38 7 83 0 55 22 6 12 26 23 65 29 1 82 84 48 95 0 32
19 10 5 71 79 18 72 8 69 78 101
The problem arises when I try to access this array after exiting the for loop with those printf() lines. This for loop (maximum i value is arbitrary) ...
for (i = 0; i < 100; i++) {
printf("%d ", decode[i]);
}
Produces this output...
29 66 31 77 11 15 2 31 79 19 78 60 26 105 101 31 73 28 14 78 19 1 11 7 78
27 1 22 69 54 0 30 1 73 100 32 84 29 29 67 51 83 78 101 82 6 0 71 84 28
13 69 77 7 4 12 83 18 60 12 30 8 73 26 9 17 79 20 76 33 26 71 43 0 5 29
71 89 17 4 9 0 100 38 7 83 0 55 22 6 12 26 23 65 29 1 82 84 48 95 0 32 19
10 5 71 79 168 187 158 23 131 127 0 0 168 187 158 23 131 127 0 0 0 0 0 0
0 0 0 0 65 0 0 0 0 0 0 0 88 187 158 23 131 127 0 0 88 187 158 23 131 127
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 64 0
0 0 0 0 0 0 16 16 0 0 0 0 0 0 72 85 73 102
Can anyone let me know what I'm doing wrong?

Answer 1

OK folks, found the issue. The function as shown here works, the issue turned out to be with a realloc() called on *decode in error in the function which handles my function above. Fixing this produced the correct results.
Guess this is a swift lesson in providing more context!