www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.learn - Can we use strings with scanf?

reply Rempas <rempas tutanota.com> writes:
For printf() we can use this format `"%.*s", cast(int)s s.length, 
s.ptr`. When trying to use the same for scanf(), it says that 
this specifier is invalid.
Jan 25 2021
parent reply Mike Parker <aldacron gmail.com> writes:
On Monday, 25 January 2021 at 09:16:11 UTC, Rempas wrote:

 For printf() we can use this format `"%.*s", cast(int)s 
 s.length, s.ptr`. When trying to use the same for scanf(), it 
 says that this specifier is invalid.


The * has a different meaning for scanf than for printf ([1] vs 
[2]).

There's also the issue that a string is immutable(char)[].

If you really, really, really, must use scanf:

```
char[bufSize] buf;
scanf("%s", buf.ptr);
```

But please don't. This is D, not 1990s C.

[1] https://www.cplusplus.com/reference/cstdio/scanf/
[2] https://www.cplusplus.com/reference/cstdio/printf/
Jan 25 2021
parent reply Rempas <rempas tutanota.com> writes:
On Monday, 25 January 2021 at 10:33:14 UTC, Mike Parker wrote:

 On Monday, 25 January 2021 at 09:16:11 UTC, Rempas wrote:

 For printf() we can use this format `"%.*s", cast(int)s 
 s.length, s.ptr`. When trying to use the same for scanf(), it 
 says that this specifier is invalid.


 The * has a different meaning for scanf than for printf ([1] vs 
 [2]).

 There's also the issue that a string is immutable(char)[].

 If you really, really, really, must use scanf:

 ```
 char[bufSize] buf;
 scanf("%s", buf.ptr);
 ```

 But please don't. This is D, not 1990s C.

 [1] https://www.cplusplus.com/reference/cstdio/scanf/
 [2] https://www.cplusplus.com/reference/cstdio/printf/


Thanks! Actually for some reason. It won't accept a char[size]. I 
created a heap allocated (with pureFree and pureMalloc) chrar*, 
then used fgets() and created an empty string and looped through 
the result adding one by one character until the '\n' which is 
not included.
Jan 25 2021
parent reply Ferhat =?UTF-8?B?S3VydHVsbXXFnw==?= <aferust gmail.com> writes:
On Monday, 25 January 2021 at 17:38:21 UTC, Rempas wrote:

 On Monday, 25 January 2021 at 10:33:14 UTC, Mike Parker wrote:

 On Monday, 25 January 2021 at 09:16:11 UTC, Rempas wrote:

 [...]


 The * has a different meaning for scanf than for printf ([1] 
 vs [2]).

 There's also the issue that a string is immutable(char)[].

 If you really, really, really, must use scanf:

 ```
 char[bufSize] buf;
 scanf("%s", buf.ptr);
 ```

 But please don't. This is D, not 1990s C.

 [1] https://www.cplusplus.com/reference/cstdio/scanf/
 [2] https://www.cplusplus.com/reference/cstdio/printf/


 Thanks! Actually for some reason. It won't accept a char[size]. 
 I created a heap allocated (with pureFree and pureMalloc) 
 chrar*, then used fgets() and created an empty string and 
 looped through the result adding one by one character until the 
 '\n' which is not included.


char[buffsize] works if buffsize is a compile time constant. Or 
just char[1024]. İt is a static array, and it's size must be 
defined at compile time.
Jan 25 2021
parent reply Rempas <rempas tutanota.com> writes:
On Monday, 25 January 2021 at 18:28:09 UTC, Ferhat Kurtulmuş 
wrote:

 On Monday, 25 January 2021 at 17:38:21 UTC, Rempas wrote:

 On Monday, 25 January 2021 at 10:33:14 UTC, Mike Parker wrote:

 [...]


 Thanks! Actually for some reason. It won't accept a 
 char[size]. I created a heap allocated (with pureFree and 
 pureMalloc) chrar*, then used fgets() and created an empty 
 string and looped through the result adding one by one 
 character until the '\n' which is not included.


 char[buffsize] works if buffsize is a compile time constant. Or 
 just char[1024]. İt is a static array, and it's size must be 
 defined at compile time.


Idk, for my it says that you can't pass dynamic arrays to scanf
Jan 25 2021
parent "H. S. Teoh" <hsteoh quickfur.ath.cx> writes:
On Mon, Jan 25, 2021 at 06:43:18PM +0000, Rempas via Digitalmars-d-learn wrote:

 On Monday, 25 January 2021 at 18:28:09 UTC, Ferhat Kurtulmuş wrote:

 On Monday, 25 January 2021 at 17:38:21 UTC, Rempas wrote:

 On Monday, 25 January 2021 at 10:33:14 UTC, Mike Parker wrote:

 [...]


 
 Thanks! Actually for some reason. It won't accept a char[size]. I
 created a heap allocated (with pureFree and pureMalloc) chrar*,
 then used fgets() and created an empty string and looped through
 the result adding one by one character until the '\n' which is not
 included.


 
 char[buffsize] works if buffsize is a compile time constant. Or just
 char[1024]. İt is a static array, and it's size must be defined at
 compile time.


 
 Idk, for my it says that you can't pass dynamic arrays to scanf


Dynamic arrays in D are "fat" pointers, they have a .ptr and .length,
but scanf expects C-style bare pointers, so you have to specify .ptr in
order to pass the pointer to scanf.  Be aware, however, that doing this
means you no longer have D's bounds-checking protection, and scanf may
cause buffer overruns if the user gives bad input.


T

-- 
Being able to learn is a great learning; being able to unlearn is a greater
learning.
Jan 25 2021