CODEWITHSUNDEEP
cwarnings
Jeff Jacob
Jeff Jacob

Reputation: 19

format '%s' expects argument of type 'char *', but argument 2 has type 'char **'

I have this C code:

#include <stdio.h>
#include <stdlib.h>
int main(){
    char *bitstr;

    printf("Enter a bitstring or q for quit: ");
    scanf("%s", &bitstr);
    return 0;
}

I keep receive the following error. What am I doing wrong? 

warning: format '%s' expects argument of type 'char *', but 
argument 2 has type 'char **' [-Wformat]

Upvotes: 1

Views: 12098

Answers (2)

chux
chux

Reputation: 154601

1 Pass address of a char array in scanf() and not the address of a char*.
2 Insure you do not overwrite your destination buffer.
3 Right-size your buffer needs. It is apparent from other posts you want a binary textual representation of an int. Let's assume your int is 8 bytes (64 bits).

#include <stdio.h>
#include <stdlib.h>
int main(){
    char bitstr[8*8 + 1];  // size to a bit representation of a big integer.
    printf("Enter a bitstring or q for quit: ");
    //Change format and pass bitscr, this results in the address of bitscr array.
    scanf("%64s", bitstr);
    return 0;
}

I prefer the fgets() & sscanf() method.

char buf[100];  // You can re-use this buffer for other inputs.
if (fgets(buf, sizeof(buf), stdin) == NULL) { ; /*handle error or EOF */ }
sscanf(buf, "%64s", bitstr);

Upvotes: 1

Mark
Mark

Reputation: 8451

Try this:

#include <stdio.h>
#include <stdlib.h>

#define MAX 100

int main(){
    char bitstr[MAX] = "";

    printf("Enter a bitstring or q for quit: ");
    scanf("%s", &bitstr);

    // or fgets(bitstr);

    return 0;
}

Try to define or allocate the size of your string/char array.

Upvotes: 0

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