why is String lost when it enters the first loop?

Question

in the following code, I ran into a problem where I had a string from getString method then it was fine until I entered the loop, then I lost the string. I don't know why I lost the sting it should be within the stack.

int main(int argc, char *argv[1]){
    char * str;
    getString(str, 100000);
    char * ID[100];
    int num[100];
    for(int i =0 ; i < 100; i ++){
        num[i]=0;
    }
    int j = 0; 
    for(int i =0; i < sizeof(str);i++){
        if( str[i] == '<'){
            char * strPoint = (str+i+1);
            int ln = findLenth(strPoint);
            char * strCom = malloc(ln*sizeof(char));
            memcpy(strCom, str, ln);
            int r = tag(ID, strCom, &j);
            if(r != -1){
                num[r]++;
            }
        }
    }
    for(int r = 0; r <j; r++){
        printf("%s     %d\n", ID[r], num[r]);
        
    }
    freeMemory(ID, j);
    return EXIT_SUCCESS;
}

void getString(char* str, int i){
    fgets (str, i, stdin);
}

`sizeof(str)` is sizeof a pointer, probably 8 (or 4), not the underlying size allocated nor the length of the string (use `strlen()` for the length) — pmg, Oct 23 '20 at 19:44
That and using the correct length function should at least get you farther. — Fred Larson, Oct 23 '20 at 19:52

score 1 · Accepted Answer · answered Oct 23 '20 at 20:01

1

First, str is uninitialized. There's no telling what it points to. You'll need to allocate some space with malloc or something and initialize str with that.

Second, your loop uses sizeof(str). While this is legal even with str uninitialized, it will not give you the length you are looking for. It will give you the size of the pointer, not what it points to. It would probably work better to call strlen(str).

answered Oct 23 '20 at 20:01

Fred Larson

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@DavidC.Rankin: `getString()` is defined at the bottom of the posted code, and allocates nothing. It also cannot modify `str` (other than locally). – Fred Larson Oct 23 '20 at 20:14
Thank you Fred! I guess I am blind in one eye and can't read out of the other.... – David C. Rankin Oct 23 '20 at 20:15

why is String lost when it enters the first loop?

1 Answers1