convertion error on C function

[Blade_792]

Ok guys i have to make a function that can take entire phrases and can be also used on while cycle.

This is my function until now:

#include <stdio.h>

char getPhrase()
{
    char phrase[1024];
    scanf("%[^\n]c", phrase);
    phrase[sizeof(phrase)-1]=0;
    return phrase;
}

 

and when used on this main:

#include <stdio.h>
#include "GetPhrase.h"

int main()
{
    char str[1024];

    for(int i=0; i<3; i++)
    {
        str=*getPhrase();
        cout<<str;
    }

    return 0;
}

give me the error: "invalid conversion from 'char*' to 'char' [-fpermissive]" in the main line where i call the function.

Any suggestion?

Edited November 29, 2020 by Blade_792
i forgot the code block sorry

[AbydosOne]

@Blade_792 The function getPhrase() needs to return char *, not char. The line in main would be str = getPhrase();

 

Also, please use CODE boxes.

[Unimportant]

2 hours ago, AbydosOne said:

@Blade_792 The function getPhrase() needs to return char *, not char. The line in main would be str = getPhrase();

 

Also, please use CODE boxes.

That wouldn't be a valid fix. The function would return a pointer to a local array that ceases to exist as soon as the function returns.

 

A solution would be to pass a pointer to str to the function for it to use.

[Dat Guy]

Bonus gotcha:

cout<<str;

Yeah, no. Won't work in C (and - technically - not even in C++ unless you pollute your namespace).

 

Seems like someone copied stuff from the web without spending a second on thinking first, to be honest.

[WereCatf]

5 hours ago, Dat Guy said:

Seems like someone copied stuff from the web without spending a second on thinking first, to be honest.

Googling is easy, understanding hard!

[Nayr438]

On 11/28/2020 at 3:17 PM, Blade_792 said:

return phrase;

This will get destroyed when the function ends making the result invalid. You need to allocate memory to store it then create a pointer.

Your also trying to store a dead pointer to a array. You can copy to an array but not assign a new value.

 

#include <stdlib.h>
#include <stdio.h>

char* getPhrase()
{    
    char* buffer = (char*) malloc(sizeof(char) * 1024);
    scanf(" %1023[^\n]c", buffer);
    return buffer;
}


int main()
{
    for(int i=0; i<3; i++)
    {
        char* phrase = getPhrase();
        printf("%s \n", phrase);
        free(phrase);
    }
    
    return 0;
}

 

or

 

#include <stdlib.h>
#include <stdio.h>

void getPhrase(char* ptr)
{    
    scanf(" %1023[^\n]c", ptr);
    return;
}


int main()
{
    char phrase[1024];
    
    for(int i=0; i<3; i++)
    {
        getPhrase(phrase);
        printf("%s \n", phrase);
    }
    
    return 0;
}

 

Edited November 30, 2020 by Nayr438
Added WereCatf's suggestion

[shadow_ray]

12 minutes ago, Nayr438 said:

char* buffer = (char*) malloc(sizeof(char));

scanf(" %[^\n]c", buffer);

ohh, 1 byte wont be enough

[wanderingfool2]

13 hours ago, Dat Guy said:

Bonus gotcha:

cout<<str;

Yeah, no. Won't work in C (and - technically - not even in C++ unless you pollute your namespace).

 

Seems like someone copied stuff from the web without spending a second on thinking first, to be honest.

Honestly though, remember how it was like when you were first just learning to code.  I'm willing to bet you could have read a line of code without knowing the ins and outs of it.  e.g. Searching "how do you write a line c", if you come across an answer like cout<<str; you might go for it without knowing better.

 

6 minutes ago, Nayr438 said:

You need to allocate memory to store it then create a pointer.

While it's true, I don't think it's necessarily good practice using malloc within functions.  I agree with @Unimportant the approach should pass the pointer in.

The dangers of using malloc in the way that was suggested is that it other than the return type there is little indication on whether memory was allocated (e.g. if it was defined in other files so you didn't immediately see the source).  For all you know, it could be using static.

 

Trying to learn, or part of an homework assignment?  I ask because if it's learning, I would suggest not using getPhrase as a function if all you intend to do is call scanf.  It's better suited to just calling scanf in the function you are using.

 

If it's homework (and thus can't change the requirement of the getPhrase function), then consider either using static or as @Unimportantsaid try malloc.

[Nayr438]

20 minutes ago, shadow_ray said:

ohh, 1 byte wont be enough

I edited, maybe that's better. I haven't touched C or most languages for that matter in quite a few years.

 

20 minutes ago, wanderingfool2 said:

The dangers of using malloc in the way that was suggested is that it other than the return type there is little indication on whether memory was allocated (e.g. if it was defined in other files so you didn't immediately see the source).  For all you know, it could be using static.

I never really worried about it as I always referenced the functions that I was calling, but I do see your point.

With that said, for such a small basic function I wouldn't personally use malloc. It was more in reference to the original code.  I did however add a second example.

[WereCatf]

3 hours ago, Nayr438 said:

#include <stdlib.h>
#include <stdio.h>

void getPhrase(char* ptr)
{    
    scanf(" %[^\n]c", ptr);
    return;
}


int main()
{
    char phrase[1024];
    
    for(int i=0; i<3; i++)
    {
        getPhrase(phrase);
        printf("%s \n", phrase);
    }
    
    return 0;
}

 

I would like to point out that you should always, ALWAYS make sure you don't overflow the buffer you're accepting user-input into. With the scanf here, it should be limited to the size of phrase minus one for the ending NULL-character.

scanf(" %1023[^\n]c", phrase);

This is an extremely good thing to learn all the way from the start.

[Blade_792]

16 hours ago, Dat Guy said:

Bonus gotcha:

cout<<str;

Yeah, no. Won't work in C (and - technically - not even in C++ unless you pollute your namespace).

 

Seems like someone copied stuff from the web without spending a second on thinking first, to be honest.

i tried to find more information as possible but i can find only useless stuff in my language even when i try go to english website

[Blade_792]

6 minutes ago, WereCatf said:

I would like to point out that you should always, ALWAYS make sure you don't overflow the buffer you're accepting user-input into. With the scanf here, it should be limited to the size of phrase minus one for the ending NULL-character.

scanf(" %1023[^\n]c", scanBuf);

This is an extremely good thing to learn all the way from the start.

i tried this way but even if it has solved the problem now it generate a new one:

"error: incopatible type assignement of 'char' to 'char [1024]'"

[Blade_792]

16 hours ago, Dat Guy said:

Bonus gotcha:

cout<<str;

Yeah, no. Won't work in C (and - technically - not even in C++ unless you pollute your namespace).

yeah i know i forgot how to use cin and cout due to some problem on my pc whit the <iostram> library and was in hurry to write due to the fact that was somthing like midnight

[WereCatf]

4 minutes ago, Blade_792 said:

i tried this way but even if it has solved the problem now it generate a new one:

"error: incopatible type assignement of 'char' to 'char [1024]'"

I have no idea what you're talking about. There is no assignment on the line you quoted.

[Dat Guy]

3 minutes ago, Blade_792 said:

i forgot how to use cin and cout

You don’t use cin and cout in C.

[Blade_792]

13 hours ago, WereCatf said:

I have no idea what you're talking about. There is no assignment on the line you quoted.

i have kinda solved using 

strcpy(str,getPhrase());

 

when i run the code it makes me enter the string once and after that it terminates without even giving the first output

[Nayr438]

2 hours ago, Blade_792 said:

i have kinda solved using 

strcpy(str,getPhrase());

 

when i run the code it makes me enter the string once and after that it terminates without even giving the first output

I posted why and 2 working examples above, with the second one being more of what you should use.

When you call "getPhrase();",  "char phrase[1024];" will never get returned. Its destroyed as soon as you hit "return phrase;" you end up returning a reference to a deleted object. Your application crashes when you try to reference the dead object.

[Blade_792]

10 hours ago, Nayr438 said:

I posted why and 2 working examples above, with the second one being more of what you should use.

When you call "getPhrase();",  "char phrase[1024];" will never get returned. Its destroyed as soon as you hit "return phrase;" you end up returning a reference to a deleted object. Your application crashes when you try to reference the dead object.

how can i solve?