Getting stange error with strings - c

Question

I'm writing a program in C for my beaglebone black to manipulate the gpio pins. This is a very crude program but its just a "beta" if you will. Just to get it up and running. My problem is that I have two character arrays. One holding a command to be passed to the system() function and another holding the path of the file that I am going to be editing, it goes to the fopen function. These character arrays are manipulated to change two numbers depending on what is passed to them from the calling function. For some reason the filename character array is being concatenated with the command. I'm skimming through the program but i don't see any obvious errors.
Here is my code
/*
* gpio.c
*
* Created on: Aug 26, 2014
* Author: Christian Macias
*
* Description: This will control your GPIO (General Purpose IO) pins on the beagle bone. Please
* ensure you are on a kernel that supports device trees.
*
* Usage: gpio(PIN, Value "1" or "0", Inverted? "0" false or "1" for true)
*
* The return value is 0 for success and -1 for failure
*
* GO UTEP!!
*/
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
int gpio(int pin, int value, int inv)
{
int sucfail=0;
int pinInt1, pinInt2=-1;
int counterOne=NULL;
char filename[28]= "/sys/class/gpio/gpio00/value";//27 characters
/*
* Checks if file is within the gpio pin range.
*/
if(pin<0 || pin>=99)
{
fprintf(stderr, "\n%s\n\t%s\n\t%s\n", "Error in gpio.c(GPIO): ", "The gpio pin selected is not "
"within the availabilty of the app", "Please select a pin from 0-99");
return -1;
}
/*
* checks to see if value is boolean aka 1 or 0
*/
if(value<0 || value>1)
{
fprintf(stderr, "\n%s\n\t%s\n\t%s", "Error in gpio.c(GPIO): ", "The Selected value is invalid", "Please"
" select a 1 or a 0");
return -1;
}
/*
* Writes the pin to a file so that it can used later
*/
FILE *PINWRITE;
PINWRITE=fopen("pinWRITE", "w+");
fprintf(PINWRITE,"%i", pin);
fclose(PINWRITE);
/*
* This section will check for pre-existence of the the PIN file to prevent errors. or
* opens it if it doesnt exist.
* First it will set up the filenames
*/
PINWRITE=fopen("pinWRITE","r");
fscanf(PINWRITE, "%1i%1i", &pinInt1, &pinInt2);//Checks the pin and sets each digit to its according variable
fclose(PINWRITE);
filename[20]='0'+pinInt1;
if(pinInt2==-1)//If it is a one digit pin, it will move the letters to fit the file name correctly and remove one of the digits
{
for(counterOne=21;counterOne<28;counterOne++)
{
filename[counterOne]=filename[counterOne+1];
}
filename[27]='\0';
}
else//If two digits it will just change the second digit
{
filename[21]='0'+pinInt2;
}
FILE *PINVALUE;//FILE pointer to the files with the value
PINVALUE=fopen(filename,"w+");
/*
* At this point the the actual checking and creation occurs
*/
char exportCommand[32]="echo 00 > /sys/class/gpio/export";//31 characters
if(PINVALUE==NULL)
{
//this runs if the file didnt exist.
exportCommand[5]='0'+pinInt1;
if(pinInt2==-1)//If it is a one digit pin, it will move the letters to fit the file name correctly and remove one of the digits
{
for(counterOne=6;counterOne<32;counterOne++)
{
exportCommand[counterOne]=exportCommand[counterOne+1];
}
exportCommand[31]='\0';
}
else//If two digits it will just change the second digit
{
exportCommand[6]='0'+pinInt2;
exportCommand[32]='\0';
}
system(exportCommand);
printf("\n%s\n", exportCommand);
printf("\n%s\n", filename);
PINVALUE=fopen(filename,"w+");
}
if(PINVALUE==NULL)
{
fprintf(stderr,"\n%s\n\t%s", "Error in gpio.c(GPIO)", "The PINVALUE (.../gpioXX/value) could not be opened");
return -1;
}
/*
* Some pins may be set up backward... on is off and off is on. To correct this we must adjust a file...
* This takes to long and i dont have the time for it so i'm doing a hot fix... sorry but its 11 and i have
* school tomorrow. The correction process it too long and i want to finish today :)
*/
if(inv==1 && value==1)
{
value=0;
}
else if(inv==1 && value==0)
{
value=1;
}
/*
* At this point the file is set up and ready to be written to.
* We will write the value now and close it.
*/
fprintf(PINVALUE, "%i", value);
fclose(PINVALUE);
return sucfail;
}

Answer 1

You are underestimating the length of string literals you want to copy into arrays, leaving no space for the nul terminator. For example, here
char filename[28]= "/sys/class/gpio/gpio00/value"; //27 characters
the literal actually has 28+1 characters (28 visible, plus a nul terminator).
You need to make the array of size 29. You can do this explicitly,
char filename[29] = "/sys/class/gpio/gpio00/value";
or implicitly:
char filename[] = "/sys/class/gpio/gpio00/value";
Similarly here, where you need the array to be of length 33:
char exportCommand[32]="echo 00 > /sys/class/gpio/export";
There may well be other errors. I would start by fixing those first. It will make finding the other ones easier.