CODEWITHSUNDEEP
cc99structure
The Gruffalo
The Gruffalo

Reputation: 355

Use of structure member operator in C

I don't understand why my C program does not compile.

The error message is:

$ gcc token_buffer.c -o token_buffer
token_buffer.c:22: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘.’ token

The first structure – token is intended to be used in many places, so I use an optional structure tag. The second structure declaration I am not reusing anywhere else so I am not using a structure tag but instead I define a variable named buffer.

And then compilation fails when I try to assign a value to one of the members of this structure.

Help?

/*
 * token_buffer.c 
 */

#include <stdio.h>
#include <stdbool.h>

/* A token is a kind-value pair */
struct token {
    char *kind;
    double value;   
};

/* A buffer for a token stream */
struct {
    bool full;
    struct token t; 
} buffer;

buffer.full = false;

main()
{
    struct token t;
    t.kind = "PLUS";
    t.value = 0;

    printf("t.kind = %s, t.value = %.2f\n", t.kind, t.value);
}

Upvotes: 1

Views: 273

Answers (3)

Jens Gustedt
Jens Gustedt

Reputation: 78923

Assignement and initialization are two different things in C. Just do

struct {
    bool full;
    struct token t; 
} buffer = { .full = false };

Upvotes: 0

P.P
P.P

Reputation: 121397

The offending part is: buffer.full = false; as you set the value outside.

Put this statement inside main().

Upvotes: 1

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726589

You cannot have free-standing operations in C: you need to put initialization into your main.

int main() { // Don't forget to make your main return int explicitly
    struct token t;
    buffer.full = false; // <---- Here it is legal

    t.kind = "PLUS";
    t.value = 0;

    printf("t.kind = %s, t.value = %.2f\n", t.kind, t.value);
    return 0; // main should return status to the operating system
}

Upvotes: 4

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