system call to write and read from a file
-1
I want to test the system call of read and write
#include <unistd.h>
#include <fcntl.h>
int main(void)
{
fd = open("/Users/me/Desktop/PubRepo/C/APUE/3.File_IO/test", O_RDWR);
write(fd, "Test the first line",20);
}
The cc reports:
In [29]: !cc write_test.c
write_test.c:6:5: error: use of undeclared identifier 'fd'
fd = open("/Users/me/Desktop/PubRepo/C/APUE/3.File_IO/test", O_RDWR);
^
write_test.c:7:11: error: use of undeclared identifier 'fd'
write(fd, "Test the first line",20)
^
2 errors generated.
I have some python basics, but have no idea how to get the code done.
c undeclared-identifier
edited Nov 13 '18 at 9:03
gsamaras
51.2k24100186
asked Nov 13 '18 at 8:53
JawSawJawSaw
4,33811735
add a comment |
-1
I want to test the system call of read and write
#include <unistd.h>
#include <fcntl.h>
int main(void)
{
fd = open("/Users/me/Desktop/PubRepo/C/APUE/3.File_IO/test", O_RDWR);
write(fd, "Test the first line",20);
}
The cc reports:
In [29]: !cc write_test.c
write_test.c:6:5: error: use of undeclared identifier 'fd'
fd = open("/Users/me/Desktop/PubRepo/C/APUE/3.File_IO/test", O_RDWR);
^
write_test.c:7:11: error: use of undeclared identifier 'fd'
write(fd, "Test the first line",20)
^
2 errors generated.
I have some python basics, but have no idea how to get the code done.
c undeclared-identifier
edited Nov 13 '18 at 9:03
gsamaras
51.2k24100186
asked Nov 13 '18 at 8:53
JawSawJawSaw
4,33811735
3
fd is not declared as said so it produces 2 errors since it has 2 usages
– TerribleDog
Nov 13 '18 at 8:55
3
When attempting to use a new language for the first time, getting to know it first is usually good (instead of just guessing and hoping for the best). Just like when learning a new spoken and written language. So please get a couple of beginners book, read some tutorials, or take a class or two, before continuing.
– Some programmer dude
Nov 13 '18 at 8:57
yes, I am taking APUE. @Someprogrammerdude
– JawSaw
Nov 13 '18 at 8:58
1
APUE is a book about programming in a Unix-like environment, but it's not a language book. It requires you to already know C.
– Some programmer dude
Nov 13 '18 at 8:59
Also, if you're reading APUE then it should have taught you to check for errors, and clean up your resources (IIRC, long time since I read it). You should check thatopenandwritesucceed. And you shouldclosethe file when you're done with it.
– Some programmer dude
Nov 13 '18 at 9:11
add a comment |
-1
-1
-1
I want to test the system call of read and write
#include <unistd.h>
#include <fcntl.h>
int main(void)
{
fd = open("/Users/me/Desktop/PubRepo/C/APUE/3.File_IO/test", O_RDWR);
write(fd, "Test the first line",20);
}
The cc reports:
In [29]: !cc write_test.c
write_test.c:6:5: error: use of undeclared identifier 'fd'
fd = open("/Users/me/Desktop/PubRepo/C/APUE/3.File_IO/test", O_RDWR);
^
write_test.c:7:11: error: use of undeclared identifier 'fd'
write(fd, "Test the first line",20)
^
2 errors generated.
I have some python basics, but have no idea how to get the code done.
c undeclared-identifier
edited Nov 13 '18 at 9:03
gsamaras
51.2k24100186
asked Nov 13 '18 at 8:53
JawSawJawSaw
4,33811735
I want to test the system call of read and write
#include <unistd.h>
#include <fcntl.h>
int main(void)
{
fd = open("/Users/me/Desktop/PubRepo/C/APUE/3.File_IO/test", O_RDWR);
write(fd, "Test the first line",20);
}
The cc reports:
In [29]: !cc write_test.c
write_test.c:6:5: error: use of undeclared identifier 'fd'
fd = open("/Users/me/Desktop/PubRepo/C/APUE/3.File_IO/test", O_RDWR);
^
write_test.c:7:11: error: use of undeclared identifier 'fd'
write(fd, "Test the first line",20)
^
2 errors generated.
I have some python basics, but have no idea how to get the code done.
c undeclared-identifier
c undeclared-identifier
edited Nov 13 '18 at 9:03
gsamaras
51.2k24100186
asked Nov 13 '18 at 8:53
JawSawJawSaw
4,33811735
edited Nov 13 '18 at 9:03
gsamaras
51.2k24100186
asked Nov 13 '18 at 8:53
JawSawJawSaw
4,33811735
edited Nov 13 '18 at 9:03
gsamaras
51.2k24100186
edited Nov 13 '18 at 9:03
gsamaras
51.2k24100186
edited Nov 13 '18 at 9:03
gsamaras
51.2k24100186
51.2k24100186
asked Nov 13 '18 at 8:53
JawSawJawSaw
4,33811735
asked Nov 13 '18 at 8:53
JawSawJawSaw
4,33811735
asked Nov 13 '18 at 8:53
JawSawJawSaw
4,33811735
4,33811735
3
fd is not declared as said so it produces 2 errors since it has 2 usages
– TerribleDog
Nov 13 '18 at 8:55
3
When attempting to use a new language for the first time, getting to know it first is usually good (instead of just guessing and hoping for the best). Just like when learning a new spoken and written language. So please get a couple of beginners book, read some tutorials, or take a class or two, before continuing.
– Some programmer dude
Nov 13 '18 at 8:57
yes, I am taking APUE. @Someprogrammerdude
– JawSaw
Nov 13 '18 at 8:58
1
APUE is a book about programming in a Unix-like environment, but it's not a language book. It requires you to already know C.
– Some programmer dude
Nov 13 '18 at 8:59
Also, if you're reading APUE then it should have taught you to check for errors, and clean up your resources (IIRC, long time since I read it). You should check thatopenandwritesucceed. And you shouldclosethe file when you're done with it.
– Some programmer dude
Nov 13 '18 at 9:11
add a comment |
3
fd is not declared as said so it produces 2 errors since it has 2 usages
– TerribleDog
Nov 13 '18 at 8:55
3
When attempting to use a new language for the first time, getting to know it first is usually good (instead of just guessing and hoping for the best). Just like when learning a new spoken and written language. So please get a couple of beginners book, read some tutorials, or take a class or two, before continuing.
– Some programmer dude
Nov 13 '18 at 8:57
yes, I am taking APUE. @Someprogrammerdude
– JawSaw
Nov 13 '18 at 8:58
1
APUE is a book about programming in a Unix-like environment, but it's not a language book. It requires you to already know C.
– Some programmer dude
Nov 13 '18 at 8:59
Also, if you're reading APUE then it should have taught you to check for errors, and clean up your resources (IIRC, long time since I read it). You should check thatopenandwritesucceed. And you shouldclosethe file when you're done with it.
– Some programmer dude
Nov 13 '18 at 9:11
3
3
fd is not declared as said so it produces 2 errors since it has 2 usages
– TerribleDog
Nov 13 '18 at 8:55
fd is not declared as said so it produces 2 errors since it has 2 usages
– TerribleDog
Nov 13 '18 at 8:55
3
3
When attempting to use a new language for the first time, getting to know it first is usually good (instead of just guessing and hoping for the best). Just like when learning a new spoken and written language. So please get a couple of beginners book, read some tutorials, or take a class or two, before continuing.
– Some programmer dude
Nov 13 '18 at 8:57
When attempting to use a new language for the first time, getting to know it first is usually good (instead of just guessing and hoping for the best). Just like when learning a new spoken and written language. So please get a couple of beginners book, read some tutorials, or take a class or two, before continuing.
– Some programmer dude
Nov 13 '18 at 8:57
yes, I am taking APUE. @Someprogrammerdude
– JawSaw
Nov 13 '18 at 8:58
yes, I am taking APUE. @Someprogrammerdude
– JawSaw
Nov 13 '18 at 8:58
1
1
APUE is a book about programming in a Unix-like environment, but it's not a language book. It requires you to already know C.
– Some programmer dude
Nov 13 '18 at 8:59
APUE is a book about programming in a Unix-like environment, but it's not a language book. It requires you to already know C.
– Some programmer dude
Nov 13 '18 at 8:59
Also, if you're reading APUE then it should have taught you to check for errors, and clean up your resources (IIRC, long time since I read it). You should check that
open and write succeed. And you should close the file when you're done with it.– Some programmer dude
Nov 13 '18 at 9:11
Also, if you're reading APUE then it should have taught you to check for errors, and clean up your resources (IIRC, long time since I read it). You should check that
open and write succeed. And you should close the file when you're done with it.– Some programmer dude
Nov 13 '18 at 9:11
add a comment |
1 Answer
1
active
oldest
votes
3
You need to declare what type fd is. What type is that? Check the reference of open(), which mentions:
int open(const char *path, int oflag, ... );
You can see that the return type is int. As a result, the variable that should be assigned the return value of that function should also be of the same type.
So change:
fd = open("/Users/me/Desktop/PubRepo/C/APUE/3.File_IO/test", O_RDWR);
to this:
int fd = open("/Users/me/Desktop/PubRepo/C/APUE/3.File_IO/test", O_RDWR);
PS: If the file doesn't exist, then you will need to do:
int fd = open("/Users/me/Desktop/PubRepo/C/APUE/3.File_IO/test", O_RDWR | O_CREAT, 0600);
Read more in Using open() to create a file in C.
answered Nov 13 '18 at 8:57
gsamarasgsamaras
51.2k24100186
2
@avirate Have you checked if the file could be opened?open()won't create a new file when you don't passO_CREAT.
– Swordfish
Nov 13 '18 at 9:07
1
@avirate if the file doesn't exist in the first place, you need to use theO_CREATas well, and a creation mode as the 3rd parameter, as @Ctx mentioned. Then if yousudo cat <yourFile>it will work. But maybe then you would like to append, but that's up to you. Read more in Using open to create files. However, I strongly suggest you to take a step back and learn some basic C first, before diving into APUE. Edit: Swordfish is right and faster than me! :)
– gsamaras
Nov 13 '18 at 9:11
1
If you use O_CREAT, you additionally should provide a creation mode as third parameter, i.e.0600
– Ctx
Nov 13 '18 at 9:12
1
thank you all for the kindness and patience, I feel and cannot say anything.
– JawSaw
Nov 13 '18 at 9:14
1
Why the downvotes?
– Ctx
Nov 13 '18 at 9:16
|
show 1 more comment
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
3
You need to declare what type fd is. What type is that? Check the reference of open(), which mentions:
int open(const char *path, int oflag, ... );
You can see that the return type is int. As a result, the variable that should be assigned the return value of that function should also be of the same type.
So change:
fd = open("/Users/me/Desktop/PubRepo/C/APUE/3.File_IO/test", O_RDWR);
to this:
int fd = open("/Users/me/Desktop/PubRepo/C/APUE/3.File_IO/test", O_RDWR);
PS: If the file doesn't exist, then you will need to do:
int fd = open("/Users/me/Desktop/PubRepo/C/APUE/3.File_IO/test", O_RDWR | O_CREAT, 0600);
Read more in Using open() to create a file in C.
answered Nov 13 '18 at 8:57
gsamarasgsamaras
51.2k24100186
2
@avirate Have you checked if the file could be opened?open()won't create a new file when you don't passO_CREAT.
– Swordfish
Nov 13 '18 at 9:07
1
@avirate if the file doesn't exist in the first place, you need to use theO_CREATas well, and a creation mode as the 3rd parameter, as @Ctx mentioned. Then if yousudo cat <yourFile>it will work. But maybe then you would like to append, but that's up to you. Read more in Using open to create files. However, I strongly suggest you to take a step back and learn some basic C first, before diving into APUE. Edit: Swordfish is right and faster than me! :)
– gsamaras
Nov 13 '18 at 9:11
1
If you use O_CREAT, you additionally should provide a creation mode as third parameter, i.e.0600
– Ctx
Nov 13 '18 at 9:12
1
thank you all for the kindness and patience, I feel and cannot say anything.
– JawSaw
Nov 13 '18 at 9:14
1
Why the downvotes?
– Ctx
Nov 13 '18 at 9:16
|
show 1 more comment
3
You need to declare what type fd is. What type is that? Check the reference of open(), which mentions:
int open(const char *path, int oflag, ... );
You can see that the return type is int. As a result, the variable that should be assigned the return value of that function should also be of the same type.
So change:
fd = open("/Users/me/Desktop/PubRepo/C/APUE/3.File_IO/test", O_RDWR);
to this:
int fd = open("/Users/me/Desktop/PubRepo/C/APUE/3.File_IO/test", O_RDWR);
PS: If the file doesn't exist, then you will need to do:
int fd = open("/Users/me/Desktop/PubRepo/C/APUE/3.File_IO/test", O_RDWR | O_CREAT, 0600);
Read more in Using open() to create a file in C.
answered Nov 13 '18 at 8:57
gsamarasgsamaras
51.2k24100186
2
@avirate Have you checked if the file could be opened?open()won't create a new file when you don't passO_CREAT.
– Swordfish
Nov 13 '18 at 9:07
1
@avirate if the file doesn't exist in the first place, you need to use theO_CREATas well, and a creation mode as the 3rd parameter, as @Ctx mentioned. Then if yousudo cat <yourFile>it will work. But maybe then you would like to append, but that's up to you. Read more in Using open to create files. However, I strongly suggest you to take a step back and learn some basic C first, before diving into APUE. Edit: Swordfish is right and faster than me! :)
– gsamaras
Nov 13 '18 at 9:11
1
If you use O_CREAT, you additionally should provide a creation mode as third parameter, i.e.0600
– Ctx
Nov 13 '18 at 9:12
1
thank you all for the kindness and patience, I feel and cannot say anything.
– JawSaw
Nov 13 '18 at 9:14
1
Why the downvotes?
– Ctx
Nov 13 '18 at 9:16
|
show 1 more comment
3
3
3
You need to declare what type fd is. What type is that? Check the reference of open(), which mentions:
int open(const char *path, int oflag, ... );
You can see that the return type is int. As a result, the variable that should be assigned the return value of that function should also be of the same type.
So change:
fd = open("/Users/me/Desktop/PubRepo/C/APUE/3.File_IO/test", O_RDWR);
to this:
int fd = open("/Users/me/Desktop/PubRepo/C/APUE/3.File_IO/test", O_RDWR);
PS: If the file doesn't exist, then you will need to do:
int fd = open("/Users/me/Desktop/PubRepo/C/APUE/3.File_IO/test", O_RDWR | O_CREAT, 0600);
Read more in Using open() to create a file in C.
answered Nov 13 '18 at 8:57
gsamarasgsamaras
51.2k24100186
You need to declare what type fd is. What type is that? Check the reference of open(), which mentions:
int open(const char *path, int oflag, ... );
You can see that the return type is int. As a result, the variable that should be assigned the return value of that function should also be of the same type.
So change:
fd = open("/Users/me/Desktop/PubRepo/C/APUE/3.File_IO/test", O_RDWR);
to this:
int fd = open("/Users/me/Desktop/PubRepo/C/APUE/3.File_IO/test", O_RDWR);
PS: If the file doesn't exist, then you will need to do:
int fd = open("/Users/me/Desktop/PubRepo/C/APUE/3.File_IO/test", O_RDWR | O_CREAT, 0600);
Read more in Using open() to create a file in C.
answered Nov 13 '18 at 8:57
gsamarasgsamaras
51.2k24100186
edited Nov 13 '18 at 9:15
answered Nov 13 '18 at 8:57
gsamarasgsamaras
51.2k24100186
answered Nov 13 '18 at 8:57
gsamarasgsamaras
51.2k24100186
answered Nov 13 '18 at 8:57
gsamarasgsamaras
51.2k24100186
51.2k24100186
2
@avirate Have you checked if the file could be opened?open()won't create a new file when you don't passO_CREAT.
– Swordfish
Nov 13 '18 at 9:07
1
@avirate if the file doesn't exist in the first place, you need to use theO_CREATas well, and a creation mode as the 3rd parameter, as @Ctx mentioned. Then if yousudo cat <yourFile>it will work. But maybe then you would like to append, but that's up to you. Read more in Using open to create files. However, I strongly suggest you to take a step back and learn some basic C first, before diving into APUE. Edit: Swordfish is right and faster than me! :)
– gsamaras
Nov 13 '18 at 9:11
1
If you use O_CREAT, you additionally should provide a creation mode as third parameter, i.e.0600
– Ctx
Nov 13 '18 at 9:12
1
thank you all for the kindness and patience, I feel and cannot say anything.
– JawSaw
Nov 13 '18 at 9:14
1
Why the downvotes?
– Ctx
Nov 13 '18 at 9:16
|
show 1 more comment
2
@avirate Have you checked if the file could be opened?open()won't create a new file when you don't passO_CREAT.
– Swordfish
Nov 13 '18 at 9:07
1
@avirate if the file doesn't exist in the first place, you need to use theO_CREATas well, and a creation mode as the 3rd parameter, as @Ctx mentioned. Then if yousudo cat <yourFile>it will work. But maybe then you would like to append, but that's up to you. Read more in Using open to create files. However, I strongly suggest you to take a step back and learn some basic C first, before diving into APUE. Edit: Swordfish is right and faster than me! :)
– gsamaras
Nov 13 '18 at 9:11
1
If you use O_CREAT, you additionally should provide a creation mode as third parameter, i.e.0600
– Ctx
Nov 13 '18 at 9:12
1
thank you all for the kindness and patience, I feel and cannot say anything.
– JawSaw
Nov 13 '18 at 9:14
1
Why the downvotes?
– Ctx
Nov 13 '18 at 9:16
2
2
@avirate Have you checked if the file could be opened?
open() won't create a new file when you don't pass O_CREAT.– Swordfish
Nov 13 '18 at 9:07
@avirate Have you checked if the file could be opened?
open() won't create a new file when you don't pass O_CREAT.– Swordfish
Nov 13 '18 at 9:07
1
1
@avirate if the file doesn't exist in the first place, you need to use the
O_CREAT as well, and a creation mode as the 3rd parameter, as @Ctx mentioned. Then if you sudo cat <yourFile> it will work. But maybe then you would like to append, but that's up to you. Read more in Using open to create files. However, I strongly suggest you to take a step back and learn some basic C first, before diving into APUE. Edit: Swordfish is right and faster than me! :)– gsamaras
Nov 13 '18 at 9:11
@avirate if the file doesn't exist in the first place, you need to use the
O_CREAT as well, and a creation mode as the 3rd parameter, as @Ctx mentioned. Then if you sudo cat <yourFile> it will work. But maybe then you would like to append, but that's up to you. Read more in Using open to create files. However, I strongly suggest you to take a step back and learn some basic C first, before diving into APUE. Edit: Swordfish is right and faster than me! :)– gsamaras
Nov 13 '18 at 9:11
1
1
If you use O_CREAT, you additionally should provide a creation mode as third parameter, i.e.
0600– Ctx
Nov 13 '18 at 9:12
If you use O_CREAT, you additionally should provide a creation mode as third parameter, i.e.
0600– Ctx
Nov 13 '18 at 9:12
1
1
thank you all for the kindness and patience, I feel and cannot say anything.
– JawSaw
Nov 13 '18 at 9:14
thank you all for the kindness and patience, I feel and cannot say anything.
– JawSaw
Nov 13 '18 at 9:14
1
1
Why the downvotes?
– Ctx
Nov 13 '18 at 9:16
Why the downvotes?
– Ctx
Nov 13 '18 at 9:16
|
show 1 more comment
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3
fd is not declared as said so it produces 2 errors since it has 2 usages
– TerribleDog
Nov 13 '18 at 8:55
3
When attempting to use a new language for the first time, getting to know it first is usually good (instead of just guessing and hoping for the best). Just like when learning a new spoken and written language. So please get a couple of beginners book, read some tutorials, or take a class or two, before continuing.
– Some programmer dude
Nov 13 '18 at 8:57
yes, I am taking APUE. @Someprogrammerdude
– JawSaw
Nov 13 '18 at 8:58
1
APUE is a book about programming in a Unix-like environment, but it's not a language book. It requires you to already know C.
– Some programmer dude
Nov 13 '18 at 8:59
Also, if you're reading APUE then it should have taught you to check for errors, and clean up your resources (IIRC, long time since I read it). You should check that
openandwritesucceed. And you shouldclosethe file when you're done with it.– Some programmer dude
Nov 13 '18 at 9:11