Passing argument 2 of strcmp makes pointer from integer without a cast

Question

void viewonechar(){

char name[25], c[25];
int n;

fp = fopen("Phonebook.txt","r");

printf ("\n\n Enter Character : ");
scanf ("%s",c);

fscanf (fp, "%s %d", name, &n);

while (!feof(fp)){

    if ((strcmp(c, name[0])) == 0){  \\ Warning in here

        printf (" %s +880%d\n",name, n);

    }

    fscanf (fp, "%s %d", name, &n);

}

printf ("\n\n");

fclose(fp);

menu();

}

When i compile the code, on the marked line this warning appears, "Passing argument 2 of strcmp makes pointer from integer without a cast". What exactly am i doing wrong?

If `name` is a `char[25]` array, what do you suppose `name[0]` is ? `strcpy` requires a `const char*` for the second parameter; `name[0]` is *not* that. — WhozCraig, Nov 14 '16 at 16:47
Note that the error message says "integer" not `int`. The `char` type (that is each array element) is an integer type. — Weather Vane, Nov 14 '16 at 16:50
What do you want to compare? Only first character of name and c? What about `if (name[0] == c[0]) {...`? Or all characters from c to the beginning of name `if (strncmp(c, name, strlen(c)) == 0) {...` — Serge Ballesta, Nov 14 '16 at 16:50
Aside: `while (!feof(fp)){` ==> `while (fscanf (fp, "%s %d", name, &n) == 2){` and remove the two other `fscanf` statements. The loop is best controlled by testing for correct conversion. — Weather Vane, Nov 14 '16 at 16:53
it is also a good habit to compile with full flags like -Wall -Wextra -Werror, as you will see exactly whats wrong — LotoLo, Nov 14 '16 at 17:05

score 1 · Accepted Answer · edited Nov 14 '16 at 16:51

1

int strcmp ( const char * str1, const char * str2 );

Since name is an array of char, name[0] is a char. strcmp takes char pointers as an arguments, so the char you have supplied is implicitly cast to an int-type and then - to the pointer, which produces an undefined behavior and most likely will lead to the segfault.

edited Nov 14 '16 at 16:51

Jonathan Leffler

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answered Nov 14 '16 at 16:49

Ari0nhh

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I want to get the first character from 'name' and compare it with c. How should i do it? – Anik Shahriar Nov 14 '16 at 16:51
@AnikShahriar: since `c` is an array too, presumably you need `if (c[0] == name[0])` to compare the two first characters. – Jonathan Leffler Nov 14 '16 at 16:52
`c` is an array as well. How you could compare set of characters with one character? – Ari0nhh Nov 14 '16 at 16:52
With `strchr` function. – Weather Vane Nov 14 '16 at 16:54
1

@AnikShahriar : If that is what you want to do, then you should ask that question. `char`s are integer types and can be compared directly with the `==` operator: `if( c[0] == name[0] )`. Possibly `c` need not be an array but just a single `char`, (i.e. `char c ;`) in which case the `scanf` should change to `scanf ("%c",&c);` – Clifford Nov 14 '16 at 17:00

score 1 · Answer 2 · edited May 23 '17 at 12:24

There are a number of problems.

Avoid scanf(). See: Why does everyone say not to use scanf? What should I use instead?. Use fgets() instead. Since you are reading just one char, char c[2] is sufficient (and also will not read in the \n character).
Always do the error checking for all the standard functions.
Your loop condition is wrong. See: Why is “while ( !feof (file) )” always wrong? You don't need to scan once outside the loop if you fix the loop.
Since you only need to compare the first chars, you can simply use c[0] == name[0].

The below code fixes the above issues:

void viewonechar(void) 
{
    char name[25], c[25];
    int n;

    FILE    fp = fopen("Phonebook.txt","r");

    if (!fp) {
        perror("fopen");
        exit(1);
    }

    printf ("\n\n Enter Character : ");
    if (fgets(c, sizeof c, stdin) == NULL) {
        fprintf(stderr, "Input error\n");
        exit(1);
    }

    while (fscanf (fp, "%24s %d", name, &n) == 2) {
        if (c[0] == name[0]) {
            printf (" %s +880%d\n",name, n);
        }  
    }
    printf ("\n\n");
    fclose(fp);
    menu();
}

Passing argument 2 of strcmp makes pointer from integer without a cast

2 Answers2