Reading input file in C - c

Question

I need to read from an input file by using C programming language to do one of my assignments.
Here's my code:
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[])
{
char *input = readFromFile(argv);
return 0;
}
char *readFromFile(char *argv[])
{
FILE *fp;
fp = fopen(argv[1],"r");
char *input, c;
int i = 0;
while(!feof(fp))
{
c = fgetc(fp);
input[i++] = c;
}
fclose(fp);
return input;
}
I want to do this reading operation in another function, not in function main(). I tried, but couldn't do it.
When I try to do it with the code above, I get an error message that says:
conflicting types for readFromFile()
How can I fix this error and do what I want?

Answer 1

You have to declare readFromFile before using it. The best way to do this is to add a prototype:
char *readFromFile(char *argv[]); /* note that the identifier is useless here */
NB: By the way, there is a lot of other errors in your source code. The main one is that you don't allocate memory for input. Therefore, you will try to dereference an unitialized pointer: this leads to an undefined behavior. Since you are returning your pointer, you need to use dynamic allocation.
#include <stdlib.h>
char *input = malloc(SIZE);
Moreover, your utilisation of feof is wrong.

Answer 2

First of all you can choose between these:
1. Declare the function prototype;
2. Declare the function before the main.
This way the function is recognized in main.To be fast I always declare function before the main.In readFromFile you aren't allocating the memory that you need, fixed it for you:
#include <stdio.h>
#include <stdlib.h>
char *readFromFile(char *argv[])
{
FILE *fp;
fp = fopen(argv[1],"r");
char *input, c;
int i = 0;
size_t size=100*sizeof(char);
input=(char*)malloc(size);
while( (c = fgetc(fp)) != EOF )
{
if(++i == size)
{
size+= 100*sizeof(char);
input=(char*)realloc(input,size);
}
input[i-1] = c;
}
fclose(fp);
return input;
}
int main(int argc, char *argv[])
{
char *input = readFromFile(argv);
return 0;
}