Dfyjkt

Im am trying to use fscanf to read through a file of hex numbers that either have a char followed by numbers or just numbers and no char. The fscanf appears to work for the first line of the file but that's it.

FILE

E10
20
22
18
E10
210
12

CODE

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

int main(int argc, char** argv) 
FILE * iFile;
char instr;
unsigned long long int address;

iFile = fopen("addresses.txt", "r");
if(iFile != NULL)

 while (fscanf(iFile, "%c%x", &instr, &address) > 0)

 printf("%c", instr); //This just works for the first line

 


fclose(iFile);
return 0;

In such cases, where you will be trying to parse the same line many times, it is better to read the line into memory, and then deal with the data in memory, rather than on disk.

char line[MAXLINE];
fgets(line, MAXLINE, iFile);

Then you have what I call the "sscanf ladder," which is a series of if-else if clauses, each of which attempts to parse line in different ways. The condition would examine the return value of sscanf, since the number of objects successfully read is the return value. So we use this number to distinguish among several different formats:

if (sscanf(line, "%c%x", &instr, &address) == 2)
 /* you have an instruction and an address */
else if (sscanf(line, "%x", &address) == 1)
 /* you have an address only */

Since, in your case, this is a loop condition, you will have to refactor this into a function of its own:

int readAtLeastAddress(const char *const line, char *instr, unsigned long long *address)

 return sscanf(line, "%c%x", instr, address) == 2 

Then you would rewrite the loop as such

while (readAtLeastAddress(line, &instr, &address)) 
 printf("%c", instr);