How to use rand — C99 version

-2

I am writing a C program and i want to use for like this :

for(int i=0 ; i < something ; i++ )

so I need to use C99 version in order to initialize the counter of for inside the " ( ) " but C99 version doesn't work with rand() function .

In fact on the man page of rand() mentions : " that the function is not part of C99 but part of POSIX "

Any ideas in order to avoid initializing the counter before for ..

//UPDATE

The output of compile is :

warning: implicit declaration of function ‘rand_r’ [-Wimplicit-function-declaration]

Code :

array[i] = rand_r(&seed) % MAX + MIN;

> array[i] type is char* (i have already dynamically allocated space for it)

Thanks

edited May 14 '15 at 6:12

paxdiablo

630k16912431665

asked May 14 '15 at 5:44

User1911

5010

rand should work just fine. Did you #include <stdlib.h>?

– user2357112
May 14 '15 at 5:48

Also, it's right there in the C99 standard, section 7.20.2.1.

– user2357112
May 14 '15 at 5:49

1

Update your question to show clearly how it doesn't work. Show us the code that falls to compile and the error message.

– Keith Thompson
May 14 '15 at 5:50

I want to declare the counter inside every for-loop because I am using many for-loops inside my program and I don't want to have many different variables every time !

– User1911
May 14 '15 at 5:55

I have updated my first post with example + code !

– User1911
May 14 '15 at 6:00

|
show 9 more comments

-2

I am writing a C program and i want to use for like this :

for(int i=0 ; i < something ; i++ )

so I need to use C99 version in order to initialize the counter of for inside the " ( ) " but C99 version doesn't work with rand() function .

In fact on the man page of rand() mentions : " that the function is not part of C99 but part of POSIX "

Any ideas in order to avoid initializing the counter before for ..

//UPDATE

The output of compile is :

warning: implicit declaration of function ‘rand_r’ [-Wimplicit-function-declaration]

Code :

array[i] = rand_r(&seed) % MAX + MIN;

> array[i] type is char* (i have already dynamically allocated space for it)

Thanks

edited May 14 '15 at 6:12

paxdiablo

630k16912431665

asked May 14 '15 at 5:44

User1911

5010

rand should work just fine. Did you #include <stdlib.h>?

– user2357112
May 14 '15 at 5:48

Also, it's right there in the C99 standard, section 7.20.2.1.

– user2357112
May 14 '15 at 5:49

1

Update your question to show clearly how it doesn't work. Show us the code that falls to compile and the error message.

– Keith Thompson
May 14 '15 at 5:50

I want to declare the counter inside every for-loop because I am using many for-loops inside my program and I don't want to have many different variables every time !

– User1911
May 14 '15 at 5:55

I have updated my first post with example + code !

– User1911
May 14 '15 at 6:00

|
show 9 more comments

-2

I am writing a C program and i want to use for like this :

for(int i=0 ; i < something ; i++ )

so I need to use C99 version in order to initialize the counter of for inside the " ( ) " but C99 version doesn't work with rand() function .

In fact on the man page of rand() mentions : " that the function is not part of C99 but part of POSIX "

Any ideas in order to avoid initializing the counter before for ..

//UPDATE

The output of compile is :

warning: implicit declaration of function ‘rand_r’ [-Wimplicit-function-declaration]

Code :

array[i] = rand_r(&seed) % MAX + MIN;

> array[i] type is char* (i have already dynamically allocated space for it)

Thanks

edited May 14 '15 at 6:12

paxdiablo

630k16912431665

asked May 14 '15 at 5:44

User1911

5010

I am writing a C program and i want to use for like this :

for(int i=0 ; i < something ; i++ )

so I need to use C99 version in order to initialize the counter of for inside the " ( ) " but C99 version doesn't work with rand() function .

In fact on the man page of rand() mentions : " that the function is not part of C99 but part of POSIX "

Any ideas in order to avoid initializing the counter before for ..

//UPDATE

The output of compile is :

warning: implicit declaration of function ‘rand_r’ [-Wimplicit-function-declaration]

Code :

array[i] = rand_r(&seed) % MAX + MIN;

> array[i] type is char* (i have already dynamically allocated space for it)

Thanks

c for-loop random c99

edited May 14 '15 at 6:12

paxdiablo

630k16912431665

asked May 14 '15 at 5:44

User1911

5010

edited May 14 '15 at 6:12

paxdiablo

630k16912431665

asked May 14 '15 at 5:44

User1911

5010

edited May 14 '15 at 6:12

paxdiablo

630k16912431665

edited May 14 '15 at 6:12

paxdiablo

630k16912431665

edited May 14 '15 at 6:12

paxdiablo

630k16912431665

asked May 14 '15 at 5:44

User1911

5010

asked May 14 '15 at 5:44

User1911

5010

asked May 14 '15 at 5:44

User1911

5010

rand should work just fine. Did you #include <stdlib.h>?

– user2357112
May 14 '15 at 5:48

Also, it's right there in the C99 standard, section 7.20.2.1.

– user2357112
May 14 '15 at 5:49

1

Update your question to show clearly how it doesn't work. Show us the code that falls to compile and the error message.

– Keith Thompson
May 14 '15 at 5:50

I want to declare the counter inside every for-loop because I am using many for-loops inside my program and I don't want to have many different variables every time !

– User1911
May 14 '15 at 5:55

I have updated my first post with example + code !

– User1911
May 14 '15 at 6:00

|
show 9 more comments

rand should work just fine. Did you #include <stdlib.h>?

– user2357112
May 14 '15 at 5:48

Also, it's right there in the C99 standard, section 7.20.2.1.

– user2357112
May 14 '15 at 5:49

1

Update your question to show clearly how it doesn't work. Show us the code that falls to compile and the error message.

– Keith Thompson
May 14 '15 at 5:50

I want to declare the counter inside every for-loop because I am using many for-loops inside my program and I don't want to have many different variables every time !

– User1911
May 14 '15 at 5:55

I have updated my first post with example + code !

– User1911
May 14 '15 at 6:00

rand should work just fine. Did you #include <stdlib.h>?

– user2357112
May 14 '15 at 5:48

Also, it's right there in the C99 standard, section 7.20.2.1.

– user2357112
May 14 '15 at 5:49

Update your question to show clearly how it doesn't work. Show us the code that falls to compile and the error message.

– Keith Thompson
May 14 '15 at 5:50

I want to declare the counter inside every for-loop because I am using many for-loops inside my program and I don't want to have many different variables every time !

– User1911
May 14 '15 at 5:55

I have updated my first post with example + code !

– User1911
May 14 '15 at 6:00

|
show 9 more comments

3 Answers
3

active

oldest

votes

rand() is very much part of the C99 standard, you just have to make sure you include the correct header file.

#include <stdlib.h>

int main(void) {

    return rand() % 10;

}

The stdlib.h header file is covered in 7.20 of the C99 standard, and rand() is covered in 7.20.2.

If your man page is stating it's not part of C99, then it's incorrect. Mine (under Debian Jessie) clearly states:

The functions rand() and srand() conform to SVr4, 4.3BSD, C89, C99, POSIX.1-2001.

But, of course, it's the standard itself which is the controlling document.

You may be misreading the man page, or whoever wrote the man page may be confused. The random() and srandom() functions are not part of C99 (they're POSIX), but rand() and srand() definitely are.

Or you may be using rand_r, the re-entrant version. That too is POSIX but not C99.

If you want to use gcc in C99 mode to get the for (int i = 0... functionality, but still want to be able to call non-C99 functions, compile with -std=gnu99 rather than -std=c99.

edited May 14 '15 at 6:06

answered May 14 '15 at 5:47

paxdiablo

630k16912431665

Thanks a lot for pointing this out ! you are right i was reading about random() and srandom() :/

– User1911
May 14 '15 at 6:02

That solved my problem.. the -std=gnu99 Thanks a lot and sorry for any inconvenience I might have caused

– User1911
May 14 '15 at 6:18

add a comment |

I'm afraid you've misunderstood several things.

rand(), rand_r(), and random() are three distinct functions.

rand() is specified by the ISO C standard, and is declared in <stdlib.h>. It's included in all editions of the C standard (1990, 1999, and 2011). That means that you can depend on any conforming hosted C implementation to provide it (by definition; any hosted implementation that doesn't implement rand() is non-conforming). (Conforming freestanding implementations are not required to provide rand(), or any library functions at all; such implementations are generally for embedded systems.)

rand_r() is not specified by the ISO C standard; instead, it's specified by the POSIX standard. POSIX defines a number of library functions on top of what ISO C defines. The fact that C99 doesn't specify rand_r() does not mean that you can't use rand_r() in a C99 program; it merely means that you can't use it in a portable C99 program. (A 100% portable C program cannot depend on POSIX, since not all implementations support POSIX.) rand_r(), like rand(), is declared (if it's declared at all) in <stdlib.h>. You may need to do something extra to enable rand_r() and other POSIX-specific functions. For gcc, you can do so by not specifying -pedantic, or by specifying -std=gnu99 (C99 with GNU extensions), or by adding

#define _POSIX_C_SOURCE 1

to the top of your source file, before the #include <stdlib.h>.

rand_r() is similar to rand(), but it's designed to be thread-safe because it uses a seed controlled by the caller rather than an implicit statically allocated seed.

Note that the POSIX standard says that rand_r() may be removed from a future POSIX standard, probably because there are much better pseudo-random number generators.

random() is yet another distinct function. It's like rand(), but somewhat more sophisticated. Like rand_r(), random() is defined by POSIX but not by ISO C. Similar considerations apply if you want to use random(). For reasons that are not entirely clear to me, you need to use different symbol (_SVID_SOURCE rather than _POSIX_C_SOURCE). As for any function, you should read the documentation to find out exactly how to use it.

None of this has anything to do with C99-style for loops. C90 does not permit loops of the form:

for (int i = 0; i < N; i ++) { /* ... */ }

That feature was added to the language by the 1999 standard (and of cource retained in the 2011 standard). This is core feature of the language, unrelated to the standard library.

To use C99-style for loops, you need to use a compiler that accepts them, possibly with a command-line option to tell it to use the 1999 standard or later.

To use a POSIX-specific function (or any library function), you need to read the documentation for the particular function and do what it says, which includes #includeing the header that defines it, possibly defining some symbol to enable it, and possibly adding extra command-line options when invoking the compiler or linker.

edited Nov 20 '18 at 2:44

answered May 14 '15 at 16:09

Keith Thompson

190k25283472

add a comment |

Use stdlib library and add following code .

#include <stdlib.h>

var_name =( rand() % 50);

answered May 14 '15 at 5:50

Arshid KV

5,41232026

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%2f30230090%2fhow-to-use-rand-c99-version%23new-answer', 'question_page');
}
);

Post as a guest

Name

Required, but never shown

3 Answers
3

active

oldest

votes

3 Answers
3

active

oldest

votes

rand() is very much part of the C99 standard, you just have to make sure you include the correct header file.

#include <stdlib.h>

int main(void) {

    return rand() % 10;

}

The stdlib.h header file is covered in 7.20 of the C99 standard, and rand() is covered in 7.20.2.

If your man page is stating it's not part of C99, then it's incorrect. Mine (under Debian Jessie) clearly states:

The functions rand() and srand() conform to SVr4, 4.3BSD, C89, C99, POSIX.1-2001.

But, of course, it's the standard itself which is the controlling document.

Or you may be using rand_r, the re-entrant version. That too is POSIX but not C99.

If you want to use gcc in C99 mode to get the for (int i = 0... functionality, but still want to be able to call non-C99 functions, compile with -std=gnu99 rather than -std=c99.

edited May 14 '15 at 6:06

answered May 14 '15 at 5:47

paxdiablo

630k16912431665

Thanks a lot for pointing this out ! you are right i was reading about random() and srandom() :/

– User1911
May 14 '15 at 6:02

That solved my problem.. the -std=gnu99 Thanks a lot and sorry for any inconvenience I might have caused

– User1911
May 14 '15 at 6:18

add a comment |

rand() is very much part of the C99 standard, you just have to make sure you include the correct header file.

#include <stdlib.h>

int main(void) {

    return rand() % 10;

}

The stdlib.h header file is covered in 7.20 of the C99 standard, and rand() is covered in 7.20.2.

If your man page is stating it's not part of C99, then it's incorrect. Mine (under Debian Jessie) clearly states:

The functions rand() and srand() conform to SVr4, 4.3BSD, C89, C99, POSIX.1-2001.

But, of course, it's the standard itself which is the controlling document.

Or you may be using rand_r, the re-entrant version. That too is POSIX but not C99.

If you want to use gcc in C99 mode to get the for (int i = 0... functionality, but still want to be able to call non-C99 functions, compile with -std=gnu99 rather than -std=c99.

edited May 14 '15 at 6:06

answered May 14 '15 at 5:47

paxdiablo

630k16912431665

Thanks a lot for pointing this out ! you are right i was reading about random() and srandom() :/

– User1911
May 14 '15 at 6:02

That solved my problem.. the -std=gnu99 Thanks a lot and sorry for any inconvenience I might have caused

– User1911
May 14 '15 at 6:18

add a comment |

rand() is very much part of the C99 standard, you just have to make sure you include the correct header file.

#include <stdlib.h>

int main(void) {

    return rand() % 10;

}

The stdlib.h header file is covered in 7.20 of the C99 standard, and rand() is covered in 7.20.2.

If your man page is stating it's not part of C99, then it's incorrect. Mine (under Debian Jessie) clearly states:

The functions rand() and srand() conform to SVr4, 4.3BSD, C89, C99, POSIX.1-2001.

But, of course, it's the standard itself which is the controlling document.

Or you may be using rand_r, the re-entrant version. That too is POSIX but not C99.

If you want to use gcc in C99 mode to get the for (int i = 0... functionality, but still want to be able to call non-C99 functions, compile with -std=gnu99 rather than -std=c99.

edited May 14 '15 at 6:06

answered May 14 '15 at 5:47

paxdiablo

630k16912431665

rand() is very much part of the C99 standard, you just have to make sure you include the correct header file.

#include <stdlib.h>

int main(void) {

    return rand() % 10;

}

The stdlib.h header file is covered in 7.20 of the C99 standard, and rand() is covered in 7.20.2.

If your man page is stating it's not part of C99, then it's incorrect. Mine (under Debian Jessie) clearly states:

The functions rand() and srand() conform to SVr4, 4.3BSD, C89, C99, POSIX.1-2001.

But, of course, it's the standard itself which is the controlling document.

Or you may be using rand_r, the re-entrant version. That too is POSIX but not C99.

If you want to use gcc in C99 mode to get the for (int i = 0... functionality, but still want to be able to call non-C99 functions, compile with -std=gnu99 rather than -std=c99.

edited May 14 '15 at 6:06

answered May 14 '15 at 5:47

paxdiablo

630k16912431665

edited May 14 '15 at 6:06

answered May 14 '15 at 5:47

paxdiablo

630k16912431665

answered May 14 '15 at 5:47

paxdiablo

630k16912431665

answered May 14 '15 at 5:47

paxdiablo

630k16912431665

Thanks a lot for pointing this out ! you are right i was reading about random() and srandom() :/

– User1911
May 14 '15 at 6:02

That solved my problem.. the -std=gnu99 Thanks a lot and sorry for any inconvenience I might have caused

– User1911
May 14 '15 at 6:18

add a comment |

Thanks a lot for pointing this out ! you are right i was reading about random() and srandom() :/

– User1911
May 14 '15 at 6:02

That solved my problem.. the -std=gnu99 Thanks a lot and sorry for any inconvenience I might have caused

– User1911
May 14 '15 at 6:18

Thanks a lot for pointing this out ! you are right i was reading about random() and srandom() :/

– User1911
May 14 '15 at 6:02

That solved my problem.. the -std=gnu99 Thanks a lot and sorry for any inconvenience I might have caused

– User1911
May 14 '15 at 6:18

add a comment |

I'm afraid you've misunderstood several things.

rand(), rand_r(), and random() are three distinct functions.

#define _POSIX_C_SOURCE 1

to the top of your source file, before the #include <stdlib.h>.

rand_r() is similar to rand(), but it's designed to be thread-safe because it uses a seed controlled by the caller rather than an implicit statically allocated seed.

Note that the POSIX standard says that rand_r() may be removed from a future POSIX standard, probably because there are much better pseudo-random number generators.

None of this has anything to do with C99-style for loops. C90 does not permit loops of the form:

for (int i = 0; i < N; i ++) { /* ... */ }

That feature was added to the language by the 1999 standard (and of cource retained in the 2011 standard). This is core feature of the language, unrelated to the standard library.

To use C99-style for loops, you need to use a compiler that accepts them, possibly with a command-line option to tell it to use the 1999 standard or later.

edited Nov 20 '18 at 2:44

answered May 14 '15 at 16:09

Keith Thompson

190k25283472

add a comment |

I'm afraid you've misunderstood several things.

rand(), rand_r(), and random() are three distinct functions.

#define _POSIX_C_SOURCE 1

to the top of your source file, before the #include <stdlib.h>.

rand_r() is similar to rand(), but it's designed to be thread-safe because it uses a seed controlled by the caller rather than an implicit statically allocated seed.

Note that the POSIX standard says that rand_r() may be removed from a future POSIX standard, probably because there are much better pseudo-random number generators.

None of this has anything to do with C99-style for loops. C90 does not permit loops of the form:

for (int i = 0; i < N; i ++) { /* ... */ }

That feature was added to the language by the 1999 standard (and of cource retained in the 2011 standard). This is core feature of the language, unrelated to the standard library.

To use C99-style for loops, you need to use a compiler that accepts them, possibly with a command-line option to tell it to use the 1999 standard or later.

edited Nov 20 '18 at 2:44

answered May 14 '15 at 16:09

Keith Thompson

190k25283472

add a comment |

I'm afraid you've misunderstood several things.

rand(), rand_r(), and random() are three distinct functions.

#define _POSIX_C_SOURCE 1

to the top of your source file, before the #include <stdlib.h>.

rand_r() is similar to rand(), but it's designed to be thread-safe because it uses a seed controlled by the caller rather than an implicit statically allocated seed.

Note that the POSIX standard says that rand_r() may be removed from a future POSIX standard, probably because there are much better pseudo-random number generators.

None of this has anything to do with C99-style for loops. C90 does not permit loops of the form:

for (int i = 0; i < N; i ++) { /* ... */ }

That feature was added to the language by the 1999 standard (and of cource retained in the 2011 standard). This is core feature of the language, unrelated to the standard library.

To use C99-style for loops, you need to use a compiler that accepts them, possibly with a command-line option to tell it to use the 1999 standard or later.

edited Nov 20 '18 at 2:44

answered May 14 '15 at 16:09

Keith Thompson

190k25283472

I'm afraid you've misunderstood several things.

rand(), rand_r(), and random() are three distinct functions.

#define _POSIX_C_SOURCE 1

to the top of your source file, before the #include <stdlib.h>.

rand_r() is similar to rand(), but it's designed to be thread-safe because it uses a seed controlled by the caller rather than an implicit statically allocated seed.

Note that the POSIX standard says that rand_r() may be removed from a future POSIX standard, probably because there are much better pseudo-random number generators.

None of this has anything to do with C99-style for loops. C90 does not permit loops of the form:

for (int i = 0; i < N; i ++) { /* ... */ }

That feature was added to the language by the 1999 standard (and of cource retained in the 2011 standard). This is core feature of the language, unrelated to the standard library.

To use C99-style for loops, you need to use a compiler that accepts them, possibly with a command-line option to tell it to use the 1999 standard or later.

edited Nov 20 '18 at 2:44

answered May 14 '15 at 16:09

Keith Thompson

190k25283472

edited Nov 20 '18 at 2:44

answered May 14 '15 at 16:09

Keith Thompson

190k25283472

answered May 14 '15 at 16:09

Keith Thompson

190k25283472

answered May 14 '15 at 16:09

Keith Thompson

190k25283472

add a comment |

Use stdlib library and add following code .

#include <stdlib.h>

var_name =( rand() % 50);

answered May 14 '15 at 5:50

Arshid KV

5,41232026

add a comment |

Use stdlib library and add following code .

#include <stdlib.h>

var_name =( rand() % 50);

answered May 14 '15 at 5:50

Arshid KV

5,41232026

add a comment |

Use stdlib library and add following code .

#include <stdlib.h>

var_name =( rand() % 50);

answered May 14 '15 at 5:50

Arshid KV

5,41232026

Use stdlib library and add following code .

#include <stdlib.h>

var_name =( rand() % 50);

answered May 14 '15 at 5:50

Arshid KV

5,41232026

answered May 14 '15 at 5:50

Arshid KV

5,41232026

answered May 14 '15 at 5:50

Arshid KV

5,41232026

answered May 14 '15 at 5:50

Arshid KV

5,41232026

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

Search This Blog

Ufyukyu