Losing values with iterative realloc in C - realloc

Question

I am working in C with Netbeans8.0
I have to read files in an iterative approach to get list of words. That is, in single iteration a file is read into an array of strings and then merge this array into a single array.
void merge_array(char** a,int* M, char** b,int N)
{
//............. Add extra memory to a ..............*/
void *tmp = realloc(a, (*M+N) * sizeof(*a));
if (tmp == NULL)
{
perror("Merging -> Could not reallocate");
exit(EXIT_FAILURE);
}
a = tmp;
memset(a+(*M), 0, N*sizeof(*a));
//............. copy strings in b to a ..............*/
int i,j=0;
for(i=*M; i<((*M)+N); i++)
{
size_t wlen = strlen(b[j]);
a[i] = malloc((wlen+1) * sizeof(char));
if (a[i] == NULL)
{
perror("Failed to replicate string");
exit(EXIT_FAILURE);
}
memcpy(a[i], b[j], wlen+1);
j++;
}
(*M) = (*M)+N; // resetting the count
printf("Confirm - %s, %d\n",a[0],*M);
}
Above function reads the contents of a file. In main above function is called iteratively and merged into a single array named 'termlist'. Main code is given below
char** termlist;
int termCount=0;
while(files[i]){
char **word_array;
int wdCnt,a;
char* tmp = (char*) malloc(strlen(path)*sizeof(char));
strcpy(tmp,path); strcat(tmp,files[i]); strcpy(files[i],tmp);
printf("\n\n******* Reading file %s...\n",files[i]);
word_array = getTerms_fscanf(files[i],&a); //reading contents of file
wdCnt = a;
if(i==0) // before reading the first file initializing the termlist
{
termlist = (char**) malloc(wdCnt*sizeof(char*));
}
merge_array(termlist,&termCount,word_array,wdCnt);
printf("CHECK - %s, %d\n",termlist[0],termCount);
free(word_array);
++i;
}
Now the problem is that,
After 1st two iterations, Inside function everything works fine but in main values of termlist[0], termlist[1] turns out to be junk.. That is first 2 words read from first file is lost. The 3rd iteration returns with failure at merge_array function call.
Output is
******* Reading F:/Netbeans C/Test Docs/doc1.txt...
Confirm - tour, 52
CHECK - tour, 52
******* Reading F:/Netbeans C/Test Docs/doc2.txt...
Confirm - tour, 71
CHECK - Ôk'aÔk'a`œ€`œ€äk'aäk'aìk'aìk'aôk'aôk'aük'aük'ah“€, 71
I am not able to identify problem with this.. Please help with this..