Why does -std=c11 with gcc hide popen in stdio.h? [duplicate]

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This question already has an answer here:

popen implicitly declared even though #include <stdio.h> is added

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I want to use popen. It is in stdio.h. I include that, but the compiler doesn't see it with
-std=c11. It does compile without -std=c11.

#include <stdio.h>



int main(void)

{

   popen("ls *","r");

}

gcc -std=c11 popen_test.c

popen_test.c: In function ‘main’:

popen_test.c:5:4: warning: implicit declaration of function ‘popen’ [-Wimplicit-function-declaration]

popen("ls *","r");

^~~~~

It is hidden in stdio.h with

#ifdef __USE_POSIX2

The man page says it is available if:

_POSIX_C_SOURCE >= 2 || /* Glibc versions <= 2.19: */
_BSD_SOURCE || _SVID_SOURCE

edited Nov 10 at 20:15

asked Nov 10 at 20:11

Scooter

3,51662749

marked as duplicate by tmlen, melpomene c
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Nov 10 at 20:19

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

popen is not part of standard C.
– melpomene
Nov 10 at 20:14

@melpomene Can you turn -std=c11 on and off in the source code?
– Scooter
Nov 10 at 20:15

What do you mean by that? Or maybe a better question: What are you trying to achieve by specifying -std=c11?
– melpomene
Nov 10 at 20:16

@melpomene I want all the features of C11
– Scooter
Nov 10 at 20:17

3

Well, e.g. -std=gnu11 would give you that plus all GNU extensions.
– melpomene
Nov 10 at 20:17

add a comment |

up vote
0
down vote

favorite

This question already has an answer here:

popen implicitly declared even though #include <stdio.h> is added

3 answers

I want to use popen. It is in stdio.h. I include that, but the compiler doesn't see it with
-std=c11. It does compile without -std=c11.

#include <stdio.h>



int main(void)

{

   popen("ls *","r");

}

gcc -std=c11 popen_test.c

popen_test.c: In function ‘main’:

popen_test.c:5:4: warning: implicit declaration of function ‘popen’ [-Wimplicit-function-declaration]

popen("ls *","r");

^~~~~

It is hidden in stdio.h with

#ifdef __USE_POSIX2

The man page says it is available if:

_POSIX_C_SOURCE >= 2 || /* Glibc versions <= 2.19: */
_BSD_SOURCE || _SVID_SOURCE

edited Nov 10 at 20:15

asked Nov 10 at 20:11

Scooter

3,51662749

marked as duplicate by tmlen, melpomene c
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Nov 10 at 20:19

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

popen is not part of standard C.
– melpomene
Nov 10 at 20:14

@melpomene Can you turn -std=c11 on and off in the source code?
– Scooter
Nov 10 at 20:15

What do you mean by that? Or maybe a better question: What are you trying to achieve by specifying -std=c11?
– melpomene
Nov 10 at 20:16

@melpomene I want all the features of C11
– Scooter
Nov 10 at 20:17

3

Well, e.g. -std=gnu11 would give you that plus all GNU extensions.
– melpomene
Nov 10 at 20:17

add a comment |

up vote
0
down vote

favorite

This question already has an answer here:

popen implicitly declared even though #include <stdio.h> is added

3 answers

I want to use popen. It is in stdio.h. I include that, but the compiler doesn't see it with
-std=c11. It does compile without -std=c11.

#include <stdio.h>



int main(void)

{

   popen("ls *","r");

}

gcc -std=c11 popen_test.c

popen_test.c: In function ‘main’:

popen_test.c:5:4: warning: implicit declaration of function ‘popen’ [-Wimplicit-function-declaration]

popen("ls *","r");

^~~~~

It is hidden in stdio.h with

#ifdef __USE_POSIX2

The man page says it is available if:

_POSIX_C_SOURCE >= 2 || /* Glibc versions <= 2.19: */
_BSD_SOURCE || _SVID_SOURCE

edited Nov 10 at 20:15

asked Nov 10 at 20:11

Scooter

3,51662749

This question already has an answer here:

popen implicitly declared even though #include <stdio.h> is added

3 answers

I want to use popen. It is in stdio.h. I include that, but the compiler doesn't see it with
-std=c11. It does compile without -std=c11.

#include <stdio.h>



int main(void)

{

   popen("ls *","r");

}

gcc -std=c11 popen_test.c

popen_test.c: In function ‘main’:

popen_test.c:5:4: warning: implicit declaration of function ‘popen’ [-Wimplicit-function-declaration]

popen("ls *","r");

^~~~~

It is hidden in stdio.h with

#ifdef __USE_POSIX2

The man page says it is available if:

_POSIX_C_SOURCE >= 2 || /* Glibc versions <= 2.19: */
_BSD_SOURCE || _SVID_SOURCE

This question already has an answer here:

popen implicitly declared even though #include <stdio.h> is added

3 answers

c popen

edited Nov 10 at 20:15

asked Nov 10 at 20:11

Scooter

3,51662749

edited Nov 10 at 20:15

asked Nov 10 at 20:11

Scooter

3,51662749

edited Nov 10 at 20:15

asked Nov 10 at 20:11

Scooter

3,51662749

asked Nov 10 at 20:11

Scooter

3,51662749

asked Nov 10 at 20:11

Scooter

3,51662749

marked as duplicate by tmlen, melpomene c
Users with the c badge can single-handedly close c questions as duplicates and reopen them as needed.

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Nov 10 at 20:19

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

marked as duplicate by tmlen, melpomene c
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Nov 10 at 20:19

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

popen is not part of standard C.
– melpomene
Nov 10 at 20:14

@melpomene Can you turn -std=c11 on and off in the source code?
– Scooter
Nov 10 at 20:15

What do you mean by that? Or maybe a better question: What are you trying to achieve by specifying -std=c11?
– melpomene
Nov 10 at 20:16

@melpomene I want all the features of C11
– Scooter
Nov 10 at 20:17

3

Well, e.g. -std=gnu11 would give you that plus all GNU extensions.
– melpomene
Nov 10 at 20:17

add a comment |

popen is not part of standard C.
– melpomene
Nov 10 at 20:14

@melpomene Can you turn -std=c11 on and off in the source code?
– Scooter
Nov 10 at 20:15

What do you mean by that? Or maybe a better question: What are you trying to achieve by specifying -std=c11?
– melpomene
Nov 10 at 20:16

@melpomene I want all the features of C11
– Scooter
Nov 10 at 20:17

3

Well, e.g. -std=gnu11 would give you that plus all GNU extensions.
– melpomene
Nov 10 at 20:17

popen is not part of standard C.
– melpomene
Nov 10 at 20:14

@melpomene Can you turn -std=c11 on and off in the source code?
– Scooter
Nov 10 at 20:15

What do you mean by that? Or maybe a better question: What are you trying to achieve by specifying -std=c11?
– melpomene
Nov 10 at 20:16

@melpomene I want all the features of C11
– Scooter
Nov 10 at 20:17

Well, e.g. -std=gnu11 would give you that plus all GNU extensions.
– melpomene
Nov 10 at 20:17

add a comment |

1 Answer
1

active

oldest

votes

up vote
1
down vote

popen is not part of C. To get it, you need to enable it with a feature test macro before including anything.

The simplest way to do it is with a #define _GNU_SOURCE at the top (or with -D_GNU_SOURCE in your compiler invocation).

compiles with -std=c11:

#define _GNU_SOURCE

#include <stdio.h>



int main(void)

{

   popen("ls *","r");

}

answered Nov 10 at 20:19

PSkocik

31.2k54568

Does -std=c11 mean "don't allow anything that isn't part of C11"? I was hoping for "allow anything that is part of C11".
– Scooter
Nov 10 at 20:20

1

@Scooter I'd say it's more like that calling gcc without a specific standards gives you some extra gnu stuff (-std=gnu11 or whatever your compiler defaults to). -std=c11 disables it so that the identifiers that the C standard says should belong to you aren't taken.
– PSkocik
Nov 10 at 20:23

2

@Scooter int popen; int main(void) { return popen; } is a valid C11 program, but it would conflict with the popen function.
– melpomene
Nov 10 at 20:24

add a comment |

1 Answer
1

active

oldest

votes

1 Answer
1

active

oldest

votes

up vote
1
down vote

popen is not part of C. To get it, you need to enable it with a feature test macro before including anything.

The simplest way to do it is with a #define _GNU_SOURCE at the top (or with -D_GNU_SOURCE in your compiler invocation).

compiles with -std=c11:

#define _GNU_SOURCE

#include <stdio.h>



int main(void)

{

   popen("ls *","r");

}

answered Nov 10 at 20:19

PSkocik

31.2k54568

Does -std=c11 mean "don't allow anything that isn't part of C11"? I was hoping for "allow anything that is part of C11".
– Scooter
Nov 10 at 20:20

1

@Scooter I'd say it's more like that calling gcc without a specific standards gives you some extra gnu stuff (-std=gnu11 or whatever your compiler defaults to). -std=c11 disables it so that the identifiers that the C standard says should belong to you aren't taken.
– PSkocik
Nov 10 at 20:23

2

@Scooter int popen; int main(void) { return popen; } is a valid C11 program, but it would conflict with the popen function.
– melpomene
Nov 10 at 20:24

add a comment |

up vote
1
down vote

popen is not part of C. To get it, you need to enable it with a feature test macro before including anything.

The simplest way to do it is with a #define _GNU_SOURCE at the top (or with -D_GNU_SOURCE in your compiler invocation).

compiles with -std=c11:

#define _GNU_SOURCE

#include <stdio.h>



int main(void)

{

   popen("ls *","r");

}

answered Nov 10 at 20:19

PSkocik

31.2k54568

Does -std=c11 mean "don't allow anything that isn't part of C11"? I was hoping for "allow anything that is part of C11".
– Scooter
Nov 10 at 20:20

1

@Scooter I'd say it's more like that calling gcc without a specific standards gives you some extra gnu stuff (-std=gnu11 or whatever your compiler defaults to). -std=c11 disables it so that the identifiers that the C standard says should belong to you aren't taken.
– PSkocik
Nov 10 at 20:23

2

@Scooter int popen; int main(void) { return popen; } is a valid C11 program, but it would conflict with the popen function.
– melpomene
Nov 10 at 20:24

add a comment |

up vote
1
down vote

popen is not part of C. To get it, you need to enable it with a feature test macro before including anything.

The simplest way to do it is with a #define _GNU_SOURCE at the top (or with -D_GNU_SOURCE in your compiler invocation).

compiles with -std=c11:

#define _GNU_SOURCE

#include <stdio.h>



int main(void)

{

   popen("ls *","r");

}

answered Nov 10 at 20:19

PSkocik

31.2k54568

popen is not part of C. To get it, you need to enable it with a feature test macro before including anything.

The simplest way to do it is with a #define _GNU_SOURCE at the top (or with -D_GNU_SOURCE in your compiler invocation).

compiles with -std=c11:

#define _GNU_SOURCE

#include <stdio.h>



int main(void)

{

   popen("ls *","r");

}

answered Nov 10 at 20:19

PSkocik

31.2k54568

answered Nov 10 at 20:19

PSkocik

31.2k54568

answered Nov 10 at 20:19

PSkocik

31.2k54568

answered Nov 10 at 20:19

PSkocik

31.2k54568

Does -std=c11 mean "don't allow anything that isn't part of C11"? I was hoping for "allow anything that is part of C11".
– Scooter
Nov 10 at 20:20

1

@Scooter I'd say it's more like that calling gcc without a specific standards gives you some extra gnu stuff (-std=gnu11 or whatever your compiler defaults to). -std=c11 disables it so that the identifiers that the C standard says should belong to you aren't taken.
– PSkocik
Nov 10 at 20:23

2

@Scooter int popen; int main(void) { return popen; } is a valid C11 program, but it would conflict with the popen function.
– melpomene
Nov 10 at 20:24

add a comment |

Does -std=c11 mean "don't allow anything that isn't part of C11"? I was hoping for "allow anything that is part of C11".
– Scooter
Nov 10 at 20:20

1

@Scooter I'd say it's more like that calling gcc without a specific standards gives you some extra gnu stuff (-std=gnu11 or whatever your compiler defaults to). -std=c11 disables it so that the identifiers that the C standard says should belong to you aren't taken.
– PSkocik
Nov 10 at 20:23

2

@Scooter int popen; int main(void) { return popen; } is a valid C11 program, but it would conflict with the popen function.
– melpomene
Nov 10 at 20:24

Does -std=c11 mean "don't allow anything that isn't part of C11"? I was hoping for "allow anything that is part of C11".
– Scooter
Nov 10 at 20:20

@Scooter I'd say it's more like that calling gcc without a specific standards gives you some extra gnu stuff (-std=gnu11 or whatever your compiler defaults to). -std=c11 disables it so that the identifiers that the C standard says should belong to you aren't taken.
– PSkocik
Nov 10 at 20:23

@Scooter int popen; int main(void) { return popen; } is a valid C11 program, but it would conflict with the popen function.
– melpomene
Nov 10 at 20:24

add a comment |

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