programming c threaded io - c++

Question

Hi what i want to do is read from a text file do something to the text and write it back out to a file. I need it to be threaded so all 3 party can run at the same time. I am trying to use a buffer to read in to and a buffer to write out from but cant work it out.
My code :
#include <stdio.h>
#include <pthread.h>
char inBuf[1000];
//char outBuf[];
void *readerFun(void *meg){
char *inputFile;
FILE *input_ptr;
inputFile = (char *) meg;
input_ptr = fopen(inputFile, "r");
if(input_ptr == NULL){
printf("%s\n", inputFile);
printf("input file not working\n");
return;
}
while(!feof(input_ptr)){
fscanf(input_ptr, "%s", &inBuf);
sleep(1);
// printf("%s\n", &inBuf );
// printf("test _____________\n" );
}
return NULL;
}
void *modifierFun(void *meg){
//char c;
//while((c = getc(inBuf) != EOF)){
//strcat(outBuf, c);
//}
//}
return NULL;
}
void *writerFun(void *meg){
char *outFile;
FILE *output_ptr;
outFile = (char *) meg;
output_ptr = fopen(outFile, "a");
while(inBuf != NULL){
printf("%s\n", inBuf );
fprintf(output_ptr, "%s", inBuf);
}
return NULL;
}
int
main (int argc, char **argv){
pthread_t reader, modifier, writer;
char *meg = argv[1];
char *meg2 = argv[2];
int ret1, ret2, ret3;
ret1 = pthread_create(&reader, NULL, readerFun, (void *) meg);
ret2 = pthread_create(&modifier, NULL, modifierFun, (void *) meg);
ret3 = pthread_create(&writer, NULL, writerFun, (void *) meg2);
pthread_join(reader, NULL);
pthread_join(modifier, NULL);
pthread_join(writer, NULL);
return 0;
}
Would be a big help is someone could point me down the right road. I have looked all over the net and cant really find what im looking for.