Alternately glibc detected free(): invalid next size (fast) [duplicate] - c

Question

This question already has answers here:
Facing an error "*** glibc detected *** free(): invalid next size (fast)"
(2 answers)
Closed 8 years ago.
Please help, I'm so new in C that I don't understand the problem
I have 3 files
main.c, set.c, set.h
in set.h
typedef struct Set{unsigned char array[16];
}Set;
in main.c
main method
int main
{
int i=0;
char *input="read_set A,0,1,2,3,4";
char *output[LEN_ACTIONS];
char *d=" ";
read_input(input, output, d,0);
char *methodName = output[0];
printf("method name:%s\n", methodName);
invoke_method(methodName, output);
for(i=0; i < LEN_ACTIONS; i++)
free(output[i]);
return 0;
}
in set.c
void read_input(char *input,char **output, char *delimiter, int onlyNumbers)
{
int index =0;
char *str =(char*)malloc(strlen(input));
strcpy(str, input);
char *tok=NULL;
tok = strtok(str,delimiter);
while(tok!=NULL)
{
char *dup = (char*)malloc(strlen(tok)+1);
if(dup)
{
if(onlyNumbers >0)
{
if(is_number(tok))
{
output[index] = strcpy(dup, tok);
index++;
}
}
else
{
output[index] = strcpy(dup, tok);
index++;
}
}
tok = strtok(NULL, delimiter);
}
free(str);
}
in main.c
void invoke_method(char *methodName, char **output)
{
int i=0;
char *d=",";
char *groups[5];
read_input(output[1], groups, d, 0);
if(strcmp(methodName,"read_set") ==0)
{
printf("group: %s\n", groups[0]);
d=",";
char *numbers[MAX_IN_SET]={NULL};
read_input(output[1], numbers, d, 1);
if(strcmp(groups[0], "A")==0)
{
printf("init A set\n");
initialize_set(&A); //initialize the array with 0
printf("input to set\n");
read_set(&A, numbers);
}
if(strcmp(groups[0], "B")==0)
{
initialize_set(&B);
read_set(&B, numbers);
}
if(strcmp(groups[0], "C")==0)
{
initialize_set(&C);
read_set(&C, numbers);
}
if(strcmp(groups[0], "D")==0)
{
initialize_set(&D);
read_set(&D, numbers);
}
if(strcmp(groups[0], "E")==0)
{
initialize_set(&E);
read_set(&E, numbers);
}
}
for(i=0; i<5; i++)
free(groups[i]);
}
in set.c
void read_set(struct Set *set, char **numbers)
{
int i=0;
for(i=0; i<MAX_IN_SET; i++)
{
if(numbers[i] != NULL && numbers[i] != '\0')
{
int number = atoi(numbers[i]);
int charIndex = number/8;
int bitIndex = number %8;
int bitPlace = 1<<(7-bitIndex);
unsigned char c = (unsigned char)bitPlace;
int numberExists = c & set->array[charIndex];
if(!numberExists)
{
set->array[charIndex] = c|set->array[charIndex];
/*printf("number %d has been added\n", number);*/
}
}
}
}
in terminal after I run this I get an error
* glibc detected* ./mainprog: free(): invalid next size (fast)
Thank you very much

Answer 1

At least one problem there:
char *str =(char*)malloc(strlen(input));
should be
char *str =(char*)malloc(strlen(input) + 1);
or better yet
char *str = strdup(input);
You're not allocating space for terminating 0, so following strcopy steps on the heap data structures.
Use valgrind to find more problems, if any.

Answer 2

A possible problem is the loop that frees the array of char*. One of them is:
for(i=0; i < LEN_ACTIONS; i++)
free(output[i]);
It depends on the input, but if there are not LEN_ACTIONS entries allocated in that array, then the free call is likely invalid because the array was not initialized to zeros (null). One possibility might be to initialize the array up front (because passing NULL to free is valid). Use something like this prior to its use:
memset(output, 0, sizeof(output));
The same potential problem exists with groups inside invoke_method.