Including a header file from another directory

问题:

I have a main directory A with two sub directories B and C.

Directory B contains a header file structures.c:

#ifndef __STRUCTURES_H
#define __STRUCTURES_H
typedef struct __stud_ent__
{
    char name[20];
    int roll_num;
}stud;
#endif

Directory C contains main.c code:

#include<stdio.h>
#include<stdlib.h>
#include <structures.h>
int main()
{
    stud *value;
    value = malloc(sizeof(stud));
    free (value);
    printf("working \n");
    return 0;
}

But I get an error:

main.c:3:24: error: structures.h: No such file or directory
main.c: In function ‘main’:
main.c:6: error: ‘stud’ undeclared (first use in this function)
main.c:6: error: (Each undeclared identifier is reported only once
main.c:6: error: for each function it appears in.)
main.c:6: error: ‘value’ undeclared (first use in this function)

What is the correct way to include the structures.h file into main.c?

回答1:

When referencing to header files relative to your c file you should use #include "path/to/header.h"

The form #include <someheader.h> is only used for internal headers or for explicitly added directories (in gcc with the -I option).

回答2:

write

#include "../b/structure.h"

in place of

#include <structures.h>

then go in directory in c & compile your main.c with

gcc main.c

回答3:

If you work on a Makefile project or simply run your code from command line, use

gcc -IC main.c

where -I option adds your C directory to the list of directories to be searched for header files, so you'll be able to use #include "structures.h"anywhere in your project.

回答4:

If you want to use the command line argument then you can give gcc -idirafter ../b/ main.c

then you don't have to do any thing inside your program.