Merging two sorted files of strings

/* stringmerge.c -- Given two sorted files of strings, it creates
*            a sorted file consisting of all their elements.
*            The names of the files are passed as command
*            line parameters.
*/

#include <stdio.h>
#define MAXBUFFER 128

int getline(FILE * fd, char buff[], int nmax){
/* It reads a line from fd and stores up to nmax of 
* its characters to buff.
*/
char c;
int n=0;

while ((c=getc(fd))!='\n'){
if(c==EOF)return EOF;
if(n<nmax)
buff[n++]=c;
}
buff[n]='\0';
return n;
}

int stringMerge(char filename1[], char filename2[] , char filename3[]) {
/* Given two sorted files of strings, called filename1 and filename2, 
* it writes their merged sequence to the file filename3.
* It returns the total number of strings written to filename3.
*/
FILE *fd1, *fd2, *fd3;
char buffer1[MAXBUFFER], buffer2[MAXBUFFER];
int ln1, ln2;
int n=0;

if ((fd1=fopen(filename1, "r"))==NULL) {
perror("fopen");
exit(1);
}
if ((fd2=fopen(filename2, "r"))==NULL) {
perror("fopen");
exit(1);
}
if ((fd3=fopen(filename3, "w"))==NULL) {
perror("fopen");
exit(1);
}

ln1 = getline(fd1,buffer1,MAXBUFFER-1);
ln2 = getline(fd2,buffer2,MAXBUFFER-1);

while ((ln1!=EOF) && (ln2!=EOF)){
if (strcmp(buffer1,buffer2)<=0){
fprintf(fd3, "%s\n", buffer1);
ln1 = getline(fd1,buffer1,MAXBUFFER-1);
}else{
fprintf(fd3, "%s\n", buffer2);
ln2 = getline(fd2,buffer2,MAXBUFFER-1);
}
n++;
}

while (ln1!=EOF){
fprintf(fd3, "%s\n", buffer1);
ln1=getline(fd1,buffer1,MAXBUFFER-1);
n++;
}

while (ln2!=EOF){
fprintf(fd3, "%s\n", buffer2);
ln2=getline(fd2,buffer2,MAXBUFFER-1);
n++;
}

fclose(fd1);
fclose(fd2);
fclose(fd3);
return n;
}

int main(int argc, char *argv[]) {
if(argc!=4){
printf("Usage: %s sortedfile1 sortedfile2 mergefile\n", argv[0]);
exit(0);
}
printf("We have %d merged records\n",
stringMerge(argv[1], argv[2], argv[3]));
}