Can printf change one of its parameters that is an array? - c

Question

Here is my code:
#define MAX_SET_LENGTH 255
typedef struct{
char name;
char *elemetns;
}Set;
void createSet();
int getString();
void filter(char raw[],int *length);
void menu();
void del_duplicate(char *s,int n);
void displyAllSets();
Set sets[26];
int setCount=0;
int main(){
menu();
}
void menu(){
int input;
do{
printf("\n1.Create Set.\n");
printf("2.display all Sets.\n");
printf("0.Exit.\n");
scanf("%d",&input);
switch(input){
case 0:
break;
case 1:
createSet();
break;
case 2:
displyAllSets();
break;
default:
printf("Error input,please input again\n");
}
}while (input!=0);
}
void displyAllSets(){
int i;
for(i=0; i<setCount; i++) {
printf("\n%c->{%s}\n",sets[i].name,sets[i].elemetns);
}
}
void createSet(){
if(setCount<26){
printf("Please input the set's elements:\n");
char elements[MAX_SET_LENGTH];
int s_length = getString(elements,MAX_SET_LENGTH);
filter(elements,&s_length);
del_duplicate(elements,s_length);
if(s_length > 0){
elements[s_length]='\0';
Set set;
set.elemetns = elements;
set.name = 'a'+ setCount;
sets[setCount++]=set;
displyAllSets();
}else{
printf("No illegal input!\n");
}
}else{
printf("It's limit to 26");
}
}
int getString(char s[],int max_length){
char c;
int i=0;
getchar();
while((c=getchar())!='\n')
s[i++]=c;
return (i>=max_length ? max_length : i);
}
void filter(char raw[],int *length){
char string[*length];
int i=0,j=0;
int deletedCount=0;
for(;i<*length;i++){
string[i]=raw[i];
}
for(i=0;i<*length;i++){
if(string[i]>='A' && string[i]<='Z'){
raw[j++]=string[i];
}else{
deletedCount++;
}
}
*length-=deletedCount;
raw[j]='\0';
}
void del_duplicate(char raw[],int length){
int i=0,j;
for(;i<length && length>0;i++){
for(j=i+1;j<length;){
if(raw[i]==raw[j]){
int delFrom=j;
while(delFrom<length){
raw[delFrom]=raw[delFrom+1];
delFrom++;
}
j=i+1;
length--;
}else{
j++;
}
}
}
}
Everything looks good when calling createSet();
but, after calling printf("\n1.Create Set.\n") in do-while block, the array sets has been modified. Can anyone help?
after pressing F6
Can you see that left bottom window, sets[0].elements gets changed, what's happening?

Answer 1

You are storing the address of a local variable on this line:
set.elemetns = elements;
That is undefined behaviour. Don't do it!
If you want to copy the string, do one of the following:
Change the structure to store a char array and use strncpy to copy the string; or
Duplicate the string (and remember to free it later): set.elemetns = strdup(elements);
In a completely separate issue, you have implemented a function getString that seems to do roughly what fgets does. You should use fgets instead.