Segfault 11 on long string, PRIOR to accessing string, only when string > 14

char[15] addend1; // not a ptr

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char *addend1 = (char *) malloc(sizeof(char) * (16) ); // pointer

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for (int j = maxlength - 1 ; j >= 0; j--)

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	#include <stdio.h>
	#include <stdlib.h>
	#include "../../c-library/include/addViaStrings.h"
	
	int main(void) {
		//	s[0] = 72; s[1] = 101; s[2] = 108; s[3] = 108; s[4] = 111; s[5] = 32; s[6] = 87; s[7] = 111; s[8] = 114; s[9] = 108; s[10] = 100; s[11] = 0;
	
		// WORKS
		// char s1[] = "14073748835532";
		// char s2[] = "14073748835532";
	
		// FAILS
		char s1[] = "140737488355328";
		char s2[] = "140737488355328";
	
		char *sum = addNumericStrings(&s1, &s2);
		printf("main.sum = %s\n", sum);
	}

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	char* addNumericStrings(char *s1, char *s2){
		// Find the length of the greater of the two
		int maxlength = findMaxLength(s1, s2);
		printf("maxlength = %d\n", maxlength); //333
	
		///////////////////////////////////////////////
		// Using malloc instead of char[maxlength] seems to have NO EFFECT on the issue
		// char addend1[maxlength]; // not a pointer
		char *addend1 = (char *) malloc(sizeof(char) * (maxlength + 1) );
		// char addend2[maxlength]; // not a pointer
		char *addend2 = (char *) malloc(sizeof(char) * (maxlength + 1) );
	
		// Allocate sum pointer
		printf("char *sum = (char *) malloc(sizeof(char) * (maxlength + 1) ) ... "); //333
		char *sum = (char *) malloc(sizeof(char) * (maxlength + 1) );
		printf("DONE\n"); //333
	
		// General use vars
		int a1, a2, total;
		int carry = 0;
	
		// Prepare the strings for manual addition. Pad the left with char 0s
		leftPad(addend1, s1, maxlength);
		leftPad(addend2, s2, maxlength);
	
		// Buffer sum with zeros
		sum[maxlength + 1] = 0; // end flag
		printf("for (int i = 0; i < (maxlength); i++) { sum[i] = '0'; } ... "); //333
		for (int i = 0; i < (maxlength); i++) { sum[i] = '0'; } // Fill w/ 0s
		printf("DONE\n"); //333
	
		// Run the manual addition
		// Start adding individual ints from end (right side)
		printf("Start adding individual ints from end (right side) ...\n"); //333
		for (int j = maxlength - 1 ; j >= 0; j--) {
			///////////////////////////////////////////
			// The segfault seems to happen BEFORE accessing addend1 or addend2
			printf("%d ..."); // 333 This DOES NOT print
			///////////////////////////////////////////
			a1 = addend1[j] - '0'; // Convert to int
			a2 = addend2[j] - '0'; // Convert to int
			total = (a1 + a2 + carry);
			carry = 0;
			if ( total >= 10){
				carry += 1;
				total -= 10;
			}
			sum[j + 1] = '0'+total; // convert to ascii value for numbers (adding 48)
		}
		sum[0] = '0' + carry; // add last carry to start of num always, even if 0
		// Before returning, truncate leading zeros
		char *returnsum = (char *) malloc(sizeof(char) * (strlen(sum) + 1) );
		int sum_i = 0;
		int returnsm_i = 0;
	//    bool truncate = true; // Find out why this wont compile
		int truncate = 1; // true
		while (1){
			// if order is important here
			if (sum[sum_i] == '\0') { break; } // we're done
			if (sum[sum_i] == '0' && truncate == 1) { sum_i += 1; continue; } // 1 is true
			// if a num, Stop truncating 0s but DO continue adding numbers
			if (sum[sum_i] != '0') { truncate = 0; } // 0 is false
			returnsum[returnsm_i] = sum[sum_i];
			returnsm_i += 1;
			sum_i += 1;
		}
		return returnsum;
	}
[\code]

[i][b]Successful run (less than 15 chars)[/b][/i]
[code]
    maxlength = 14
    char *sum = (char *) malloc(sizeof(char) * (maxlength + 1) ) ... DONE
    for (int i = 0; i < (maxlength); i++) { sum[i] = '0'; } ... DONE
    Start adding individual ints from end (right side) ...
    13 ...12 ...11 ...10 ...9 ...8 ...7 ...6 ...5 ...4 ...3 ...2 ...1 ...0 ...main.sum = 28147497671064

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    maxlength = 15
    char *sum = (char *) malloc(sizeof(char) * (maxlength + 1) ) ... DONE
    for (int i = 0; i < (maxlength); i++) { sum[i] = '0'; } ... DONE
    Start adding individual ints from end (right side) ...

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