error: unknown type name struct

Question

I'm trying to solve Conway's Game of Life in C. I have written a .h file containing all my functions, yet I receive the following error within the header file: error: unknown type name "matrix"

This is the beginning of the header file, which contains my struct declaration and the 1st function:

#include<stdio.h>
#include<string.h>
#define MAX 1000
struct matrix{
    int Val, Next;
};
void intro_date(int nr_elem, matrix a[MAX][MAX]){
    int x,y;
    printf("Enter the line and the column of the element which you wish to read within the matrix: \n");
    while(nr_elem){
        scanf("%d%d",&x,&y);
        a[x][y].Val=1;
        --nr_elem;
    }
}

In C you can not ommit the `struct` keyword, `matrix a[MAX][MAX]` should be `struct matrix a[MAX][MAX]` (or use a `typedef`) — David Ranieri, Nov 02 '16 at 17:42
Here is explained: http://stackoverflow.com/questions/1675351/typedef-struct-vs-struct-definitions — germanfr, Nov 02 '16 at 17:44
Or the definition should be `typedef struct matrix{ int Val, Next; } matrix;`. — JohnB, Nov 02 '16 at 17:44
You should not put function implementations in C header files, only their prototypes. Including the implementation as well tends to produce duplicate definitions, which are not allowed. — John Bollinger, Nov 02 '16 at 17:45

score 7 · Accepted Answer · answered Nov 02 '16 at 18:05

You defined a structure called struct matrix. This is not the same as matrix, as struct definitions must be preceeded by the struct keyword.

Change your function definition to:

void intro_date(int nr_elem, struct matrix a[MAX][MAX])

Also, you should not put code into a header file. Only type definitions and declarations belong there. If more than one source file were to include this header, the object file created for each will contain a copy of the function intro_date(). Upon attempting to link those files, you'll get an error stating intro_date() was redefined.

The definition of intro_date should exist in exactly one source file. Then the header would contain just the declaration.

Armen Yeganyan · Answer 2 · 2018-03-13T10:36:39.703

2

Typedef on struct declaration its "new name".

typedef struct matrix{
    int Val, Next;
} matrix;

Or specify on new instance creation explictly that it is struct:

struct matrix a[MAX][MAX];

edited Mar 13 '18 at 10:36

answered Nov 02 '16 at 17:44

Armen Yeganyan

89
8

score 1 · Answer 3 · answered Nov 02 '16 at 17:51

1

Instead of

    void intro_date(int nr_elem, matrix a[MAX][MAX]){

use

    void intro_date(int nr_elem, struct matrix a[MAX][MAX]){

answered Nov 02 '16 at 17:51

MarianD

13,096
12
42
54

score 0 · Answer 4 · answered Jan 12 '21 at 14:54

0

Use Struct Keyword before that.

For C compilers, you have to user struct keyword whereas In C++, the struct keyword is optional. For Ease in C, you can typedef it.

typedef struct _matrix{
    int Val, Next;
}matrix;

answered Jan 12 '21 at 14:54

Gurpreet Singh

107
1
2

error: unknown type name struct

4 Answers4

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