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
– WhozCraig, Commented Nov 14, 2016 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
– Weather Vane, Commented Nov 14, 2016 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
– Serge Ballesta, Commented Nov 14, 2016 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
– Weather Vane, Commented Nov 14, 2016 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
– LotoLo, Commented Nov 14, 2016 at 17:05

Jonathan Leffler · Accepted Answer · 2016-11-14 16:51:38Z

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, 2016 at 16:51

Jonathan Leffler

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answered Nov 14, 2016 at 16:49

Ari0nhh

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5 Comments

Anik Shahriar Over a year ago

I want to get the first character from 'name' and compare it with c. How should i do it?

Jonathan Leffler Over a year ago

@AnikShahriar: since c is an array too, presumably you need if (c[0] == name[0]) to compare the two first characters.

Ari0nhh Over a year ago

c is an array as well. How you could compare set of characters with one character?

Weather Vane Over a year ago

With strchr function.

Clifford Over a year ago

@AnikShahriar : If that is what you want to do, then you should ask that question. chars 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);

Community · Accepted Answer · 2017-05-23 12:24:44Z

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();
}

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