array of structure pointers

So I have 3 files: main.c,countries.h and countries.c

I declare pointer of the structure called "Country" in the countries.h

I have included the countries.h in countries.c and in main.c

and declared the structure its self in countries.c

countries.h

typedef struct Country* pCountry;

countries.c

struct Country {

    char *name;

    pCity cities;

    int numCities;

    pTerritory countryTerr;

};

now, I want to create array of pointers of the Country structure, using malloc

so I did that:

pCountry countries_array;

countries_array = (pCountry); 

malloc(num_of_countries*sizeof(countries_array));

and to assign pointers to each pointer,even though the malloc, does seems to work I cant

assign pointers to the elements in the array using :

countries_array[0]= new_pointer;

I get "invalid use of undefine struct country" and "derefrecing pointer to incomplete",

what is the problem with the code?

thanks

edited Nov 22 '18 at 0:28

Tico

2,07712332

asked Nov 21 '18 at 22:44

kal pola

111

2

malloc() returns a value.

– wildplasser
Nov 21 '18 at 22:46

2

malloc itselfs returns the pointer, NULL if there is no memory available like: countries_array = malloc(num_of_countries*sizeof countries_array);

– Tom Kuschel
Nov 21 '18 at 22:48

2

You will want to review: Is it a good idea to typedef pointers?.

– David C. Rankin
Nov 21 '18 at 23:00

What is countries_array = (pCountry); supposed to mean? Was that intended to be a type cast of the result of the next line?

– Barmar
Nov 21 '18 at 23:42

which file does the error point to, to which line? how declaration of the country_array looks like?

– Serge
Nov 22 '18 at 2:33

add a comment |

So I have 3 files: main.c,countries.h and countries.c

I declare pointer of the structure called "Country" in the countries.h

I have included the countries.h in countries.c and in main.c

and declared the structure its self in countries.c

countries.h

typedef struct Country* pCountry;

countries.c

struct Country {

    char *name;

    pCity cities;

    int numCities;

    pTerritory countryTerr;

};

now, I want to create array of pointers of the Country structure, using malloc

so I did that:

pCountry countries_array;

countries_array = (pCountry); 

malloc(num_of_countries*sizeof(countries_array));

and to assign pointers to each pointer,even though the malloc, does seems to work I cant

assign pointers to the elements in the array using :

countries_array[0]= new_pointer;

I get "invalid use of undefine struct country" and "derefrecing pointer to incomplete",

what is the problem with the code?

thanks

edited Nov 22 '18 at 0:28

Tico

2,07712332

asked Nov 21 '18 at 22:44

kal pola

111

2

malloc() returns a value.

– wildplasser
Nov 21 '18 at 22:46

2

malloc itselfs returns the pointer, NULL if there is no memory available like: countries_array = malloc(num_of_countries*sizeof countries_array);

– Tom Kuschel
Nov 21 '18 at 22:48

2

You will want to review: Is it a good idea to typedef pointers?.

– David C. Rankin
Nov 21 '18 at 23:00

What is countries_array = (pCountry); supposed to mean? Was that intended to be a type cast of the result of the next line?

– Barmar
Nov 21 '18 at 23:42

which file does the error point to, to which line? how declaration of the country_array looks like?

– Serge
Nov 22 '18 at 2:33

add a comment |

So I have 3 files: main.c,countries.h and countries.c

I declare pointer of the structure called "Country" in the countries.h

I have included the countries.h in countries.c and in main.c

and declared the structure its self in countries.c

countries.h

typedef struct Country* pCountry;

countries.c

struct Country {

    char *name;

    pCity cities;

    int numCities;

    pTerritory countryTerr;

};

now, I want to create array of pointers of the Country structure, using malloc

so I did that:

pCountry countries_array;

countries_array = (pCountry); 

malloc(num_of_countries*sizeof(countries_array));

and to assign pointers to each pointer,even though the malloc, does seems to work I cant

assign pointers to the elements in the array using :

countries_array[0]= new_pointer;

I get "invalid use of undefine struct country" and "derefrecing pointer to incomplete",

what is the problem with the code?

thanks

edited Nov 22 '18 at 0:28

Tico

2,07712332

asked Nov 21 '18 at 22:44

kal pola

111

So I have 3 files: main.c,countries.h and countries.c

I declare pointer of the structure called "Country" in the countries.h

I have included the countries.h in countries.c and in main.c

and declared the structure its self in countries.c

countries.h

typedef struct Country* pCountry;

countries.c

struct Country {

    char *name;

    pCity cities;

    int numCities;

    pTerritory countryTerr;

};

now, I want to create array of pointers of the Country structure, using malloc

so I did that:

pCountry countries_array;

countries_array = (pCountry); 

malloc(num_of_countries*sizeof(countries_array));

and to assign pointers to each pointer,even though the malloc, does seems to work I cant

assign pointers to the elements in the array using :

countries_array[0]= new_pointer;

I get "invalid use of undefine struct country" and "derefrecing pointer to incomplete",

what is the problem with the code?

thanks

c pointers

edited Nov 22 '18 at 0:28

Tico

2,07712332

asked Nov 21 '18 at 22:44

kal pola

111

edited Nov 22 '18 at 0:28

Tico

2,07712332

asked Nov 21 '18 at 22:44

kal pola

111

edited Nov 22 '18 at 0:28

Tico

2,07712332

edited Nov 22 '18 at 0:28

Tico

2,07712332

edited Nov 22 '18 at 0:28

Tico

2,07712332

asked Nov 21 '18 at 22:44

kal pola

111

asked Nov 21 '18 at 22:44

kal pola

111

asked Nov 21 '18 at 22:44

kal pola

111

2

malloc() returns a value.

– wildplasser
Nov 21 '18 at 22:46

2

malloc itselfs returns the pointer, NULL if there is no memory available like: countries_array = malloc(num_of_countries*sizeof countries_array);

– Tom Kuschel
Nov 21 '18 at 22:48

2

You will want to review: Is it a good idea to typedef pointers?.

– David C. Rankin
Nov 21 '18 at 23:00

What is countries_array = (pCountry); supposed to mean? Was that intended to be a type cast of the result of the next line?

– Barmar
Nov 21 '18 at 23:42

which file does the error point to, to which line? how declaration of the country_array looks like?

– Serge
Nov 22 '18 at 2:33

add a comment |

2

malloc() returns a value.

– wildplasser
Nov 21 '18 at 22:46

2

malloc itselfs returns the pointer, NULL if there is no memory available like: countries_array = malloc(num_of_countries*sizeof countries_array);

– Tom Kuschel
Nov 21 '18 at 22:48

2

You will want to review: Is it a good idea to typedef pointers?.

– David C. Rankin
Nov 21 '18 at 23:00

What is countries_array = (pCountry); supposed to mean? Was that intended to be a type cast of the result of the next line?

– Barmar
Nov 21 '18 at 23:42

which file does the error point to, to which line? how declaration of the country_array looks like?

– Serge
Nov 22 '18 at 2:33

malloc() returns a value.

– wildplasser
Nov 21 '18 at 22:46

malloc itselfs returns the pointer, NULL if there is no memory available like: countries_array = malloc(num_of_countries*sizeof countries_array);

– Tom Kuschel
Nov 21 '18 at 22:48

You will want to review: Is it a good idea to typedef pointers?.

– David C. Rankin
Nov 21 '18 at 23:00

What is countries_array = (pCountry); supposed to mean? Was that intended to be a type cast of the result of the next line?

– Barmar
Nov 21 '18 at 23:42

which file does the error point to, to which line? how declaration of the country_array looks like?

– Serge
Nov 22 '18 at 2:33

add a comment |

1 Answer
1

active

oldest

votes

Looks good. Just assign it to something of the same type, struct Country. Also, as pointed out in the comments, it should be malloc num_of_countries * sizeof struct Country (not the pointer type), which is now correctly dereferenced below as sizeof (*countries_array) which also works.

pCountry countries_array;

countries_array = malloc(num_of_countries * sizeof (*countries_array));

struct Country Jefferson = {"Jefferson", 1,2,3 };

countries_array[0] = Jefferson;



// don't forget to free the memory when no longer needed.

free (countries_array);

If we must put a pointer into this array of structs, we can either dereference the pointer like countries_array[0] = *pointer, or... we could declare countries_array as an array of pointers, instead of an array of structs. Perhaps this is what you may want. Either way, the actual structures have to occupy memory somewhere...

pCountry *countries_array = malloc(num_of_countries*sizeof countries_array);

pCountry j = &Jefferson; // `&`, "address of" operator

countries_array[0] = j; // put a `pointer` into the array...

edited Nov 23 '18 at 7:18

answered Nov 21 '18 at 23:39

hellork

935

Checking right after malloc for out of memory condition is advisable. if (!countries_array) { fprintf(stderr, "out of memory"); exit 1; }

– hellork
Nov 21 '18 at 23:46

On casting malloc(). Since this is tagged "C" we don't (cast) the result of malloc, because it hides important compiler errors if we do. In C++, it is required, so it crops up quite a bit. c-faq.com/malloc/mallocnocast.html

– hellork
Nov 22 '18 at 0:10

add a comment |

Your Answer

StackExchange.ifUsing("editor", function () {
StackExchange.using("externalEditor", function () {
StackExchange.using("snippets", function () {
StackExchange.snippets.init();
});
});
}, "code-snippets");

StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "1"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});

function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});

}
});

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53421469%2farray-of-structure-pointers%23new-answer', 'question_page');
}
);

Post as a guest

Name

Required, but never shown

1 Answer
1

active

oldest

votes

1 Answer
1

active

oldest

votes

pCountry countries_array;

countries_array = malloc(num_of_countries * sizeof (*countries_array));

struct Country Jefferson = {"Jefferson", 1,2,3 };

countries_array[0] = Jefferson;



// don't forget to free the memory when no longer needed.

free (countries_array);

pCountry *countries_array = malloc(num_of_countries*sizeof countries_array);

pCountry j = &Jefferson; // `&`, "address of" operator

countries_array[0] = j; // put a `pointer` into the array...

edited Nov 23 '18 at 7:18

answered Nov 21 '18 at 23:39

hellork

935

Checking right after malloc for out of memory condition is advisable. if (!countries_array) { fprintf(stderr, "out of memory"); exit 1; }

– hellork
Nov 21 '18 at 23:46

On casting malloc(). Since this is tagged "C" we don't (cast) the result of malloc, because it hides important compiler errors if we do. In C++, it is required, so it crops up quite a bit. c-faq.com/malloc/mallocnocast.html

– hellork
Nov 22 '18 at 0:10

add a comment |

pCountry countries_array;

countries_array = malloc(num_of_countries * sizeof (*countries_array));

struct Country Jefferson = {"Jefferson", 1,2,3 };

countries_array[0] = Jefferson;



// don't forget to free the memory when no longer needed.

free (countries_array);

pCountry *countries_array = malloc(num_of_countries*sizeof countries_array);

pCountry j = &Jefferson; // `&`, "address of" operator

countries_array[0] = j; // put a `pointer` into the array...

edited Nov 23 '18 at 7:18

answered Nov 21 '18 at 23:39

hellork

935

Checking right after malloc for out of memory condition is advisable. if (!countries_array) { fprintf(stderr, "out of memory"); exit 1; }

– hellork
Nov 21 '18 at 23:46

On casting malloc(). Since this is tagged "C" we don't (cast) the result of malloc, because it hides important compiler errors if we do. In C++, it is required, so it crops up quite a bit. c-faq.com/malloc/mallocnocast.html

– hellork
Nov 22 '18 at 0:10

add a comment |

pCountry countries_array;

countries_array = malloc(num_of_countries * sizeof (*countries_array));

struct Country Jefferson = {"Jefferson", 1,2,3 };

countries_array[0] = Jefferson;



// don't forget to free the memory when no longer needed.

free (countries_array);

pCountry *countries_array = malloc(num_of_countries*sizeof countries_array);

pCountry j = &Jefferson; // `&`, "address of" operator

countries_array[0] = j; // put a `pointer` into the array...

edited Nov 23 '18 at 7:18

answered Nov 21 '18 at 23:39

hellork

935

pCountry countries_array;

countries_array = malloc(num_of_countries * sizeof (*countries_array));

struct Country Jefferson = {"Jefferson", 1,2,3 };

countries_array[0] = Jefferson;



// don't forget to free the memory when no longer needed.

free (countries_array);

pCountry *countries_array = malloc(num_of_countries*sizeof countries_array);

pCountry j = &Jefferson; // `&`, "address of" operator

countries_array[0] = j; // put a `pointer` into the array...

edited Nov 23 '18 at 7:18

answered Nov 21 '18 at 23:39

hellork

935

edited Nov 23 '18 at 7:18

answered Nov 21 '18 at 23:39

hellork

935

answered Nov 21 '18 at 23:39

hellork

935

answered Nov 21 '18 at 23:39

hellork

935

Checking right after malloc for out of memory condition is advisable. if (!countries_array) { fprintf(stderr, "out of memory"); exit 1; }

– hellork
Nov 21 '18 at 23:46

On casting malloc(). Since this is tagged "C" we don't (cast) the result of malloc, because it hides important compiler errors if we do. In C++, it is required, so it crops up quite a bit. c-faq.com/malloc/mallocnocast.html

– hellork
Nov 22 '18 at 0:10

add a comment |

Checking right after malloc for out of memory condition is advisable. if (!countries_array) { fprintf(stderr, "out of memory"); exit 1; }

– hellork
Nov 21 '18 at 23:46

On casting malloc(). Since this is tagged "C" we don't (cast) the result of malloc, because it hides important compiler errors if we do. In C++, it is required, so it crops up quite a bit. c-faq.com/malloc/mallocnocast.html

– hellork
Nov 22 '18 at 0:10

Checking right after malloc for out of memory condition is advisable. if (!countries_array) { fprintf(stderr, "out of memory"); exit 1; }

– hellork
Nov 21 '18 at 23:46

On casting malloc(). Since this is tagged "C" we don't (cast) the result of malloc, because it hides important compiler errors if we do. In C++, it is required, so it crops up quite a bit. c-faq.com/malloc/mallocnocast.html

– hellork
Nov 22 '18 at 0:10

add a comment |

draft saved

draft discarded

Thanks for contributing an answer to Stack Overflow!

Please be sure to answer the question. Provide details and share your research!

But avoid …

Asking for help, clarification, or responding to other answers.

Making statements based on opinion; back them up with references or personal experience.

To learn more, see our tips on writing great answers.

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Name

Required, but never shown

Name

Required, but never shown

This page is only for reference, If you need detailed information, please check here

搜尋此網誌

Ytukyg