Why is this string empty? - c

Question

I have this little problem, and can't solve it.
The thing is that I'm trying to load all four strings in the function LOAD by asking the user to insert it. Everything seems fine and I don't get any compiler error. But eaf stays empty. I tried many ways, even replacing scanf with gets, gets_s, fgets, but nothing changes.
#include <conio.h>
#include <stdio.h>
#include <string.h>
void LOAD(char eaf[], char initials[], char finals[], char symbols[]);
int COMPARE(char s[], char eaf[]);
int main()
{
char eaf[10],initials[1],finals[10],symbols[5];
LOAD(eaf, initials, finals, symbols);
return 0;
}
void LOAD(char eaf[], char initials[], char finals[], char symbols[])
{
printf("Insert states of the optimized AFD\n");
scanf( " %s", eaf);
printf("Insert AFD initial state\n");
do
{
scanf( " %s", initials);
} while (COMPARE(initials, eaf));
printf("Insert final state(s)\n");
do
{
scanf( " %s",finals);
} while (COMPARE(finals, eaf));
printf("Insert the language symbols\n");
scanf( " %s",symbols);
}
int COMPARE(char s[], char eaf[])
{
int i;
char *ptr;
for(i; i < strlen(s); i++){
printf("%d\n", i);
while(ptr==NULL){
ptr = strchr(eaf, *s);
}
}
if (ptr == NULL) return 1;
else return 0;
}
What am I doing wrong? This is just a small part of a bigger program, but the rest of it is useless because eaf is empty. I thought that the problem was using scanf, but as I said other functions didn't work as well. I hope anyone can help me. Thanks
edit: I checked by strlen(eaf)

Answer 1

Using "scanf" for input is dangerous, and you've walked right into that danger. You're allowing it to overwrite the contents of "eaf" when you ask it to read initials as a string and it adds the terminating 0.
Ultimately, the string is empty because you got your array dimensions wrong. You gave "initials" an array size of 1 which does not provide space for the trailing '\0' C-string terminator.
See the live demo of this code on ideone:
#include <stdio.h>
void report(char* eaf, char* initials, char* foo)
{
printf("eaf = %p, initials = %p, foo = %p\n", eaf, initials, foo);;
printf("*eaf = %d, *initials = %d, *foo = %d\n", eaf[0], initials[0], foo[0]);
}
void load(char eaf[], char initials[], char foo[])
{
printf("load\n");
report(eaf, initials, foo);
printf("Enter EAF\n");
scanf(" %s", eaf);
report(eaf, initials, foo);
printf("Enter initial state\n");
scanf(" %s", initials);
report(eaf, initials, foo);
}
int main(int argc, const char* argv[])
{
char eaf[10], initials[1], foo[10];
report(eaf, initials, foo);
load(eaf, initials, foo);
report(eaf, initials, foo);
return 0;
}
You should have walked thru this in the debugger and watched the values of "eaf" and "initials" to see what happened as you progressed.
Do you have to write this program in C? It seems that using a scripting language such as perl or python might be easier for you.
Here is a working C method to start solving the problem, note that I didn't actually fix the problem, but it will make it easier to see it.
#include <stdio.h>
#include <assert.h>
#include <stdlib.h>
#include <string.h>
void report(char* eaf, char* initials, char* foo)
{
printf("eaf = %p, initials = %p, foo = %p\n", eaf, initials, foo);;
printf("*eaf = %d, *initials = %d, *foo = %d\n", eaf[0], initials[0], foo[0]);
}
void load(const char* label, const char* into, size_t intoSize)
{
assert(intoSize > 1); // can't store a string in 1 character.
printf("%s\n", label);
char input[1024] = "";
fgets(input, sizeof(input), stdin);
size_t len = strlen(input);
// strip trailing \n off.
if (len > 0 && input[len - 1] == '\n') {
input[--len] = 0;
}
// abort on empty input
if (len <= 0) {
fprintf(stderr, "Invalid input - terminated.\n");
exit(1);
}
if (len >= intoSize) {
fprintf(stderr, "Invalid input - length was %u, limit is %u\n", len, intoSize - 1);
exit(2);
}
strncpy(into, input, intoSize);
}
int main(int argc, const char* argv[])
{
char eaf[10], initials[1], foo[10];
report(eaf, initials, foo);
load("Insert states of the optimized AFD", eaf, sizeof(eaf));
report(eaf, initials, foo);
load("Insert initial AFD state", initials, sizeof(initials));
report(eaf, initials, foo);
printf("eaf = %s\ninitials = %s\n", eaf, initials);
return 0;
}
See live demo on ideone here.

Answer 2

You're format string in scanf is most likely the culprit; you have an extra space before the %s.
Change:
scanf( " %s", eaf);
to
scanf( "%s", eaf);
for all your scanf's.
Its not putting your input into eaf because it is looking for a string of the format " blahblahblah" (note the space in the beginning) instead of "blahblahblah"
Edit
Disregard the above,
whitespace: Any whitespace characters trigger a scan for zero or more whitespace characters. The number and type of whitespace characters do not need to match in either direction.
Also, you should initialize i in your COMPARE function (I don't understand how you're not getting an angry warning from your compiler), I ran your code with no modifications and strlen(eaf) returned the correct count (just after the scanf).