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"Use of possibly unassigned field" compile error

Our company has been developing a program in C# for some time now, and we
haven't had any problems with it, but just last night something cropped up
that has me, and everyone else, stumped.

I have a struct that contains several different types of data. This struct
is used throuout the program. Now, when I compile, I get 6 errors, all of
them "Use of possibly unassigned field 'awayTime'" or "Use of possibly
unassigned field 'intlTime'". It is correct, it is possible that these
fields aren't assigned, but I don't care. It's inside of a struct, and
everything inside of a struct gets assigned its default value anyway.

This is difficult to explain, but if anyone else has had this problem and
fixed it, i'd love to know how. Thanks.

Chris LaJoie
Nov 15 '05 #1
10 19723
Chris LaJoie <ch***@etriptra der.com> wrote:
Our company has been developing a program in C# for some time now, and we
haven't had any problems with it, but just last night something cropped up
that has me, and everyone else, stumped.

I have a struct that contains several different types of data. This struct
is used throuout the program. Now, when I compile, I get 6 errors, all of
them "Use of possibly unassigned field 'awayTime'" or "Use of possibly
unassigned field 'intlTime'". It is correct, it is possible that these
fields aren't assigned, but I don't care. It's inside of a struct, and
everything inside of a struct gets assigned its default value anyway.
Local variables *don't* have default values, according to the C# spec.
That's what you're running into.
This is difficult to explain, but if anyone else has had this problem and
fixed it, i'd love to know how. Thanks.


The easiest way to fix it is to change:

MyStruct foo;

to

MyStruct foo = new MyStruct();

in your code.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
Nov 15 '05 #2
The struct var was being used inside of a foreach loop. Just for kicks (a
hunch) I changed the foreach to a for, looping through the array. This
solved everything.

Simply using bla = new StructName() would not have worked in this case
(because the values were being read from, not assigned to).

Chris LaJoie

"Jon Skeet" <sk***@pobox.co m> wrote in message
news:MP******** *************** *@news.microsof t.com...
Chris LaJoie <ch***@etriptra der.com> wrote:
Our company has been developing a program in C# for some time now, and we haven't had any problems with it, but just last night something cropped up that has me, and everyone else, stumped.

I have a struct that contains several different types of data. This struct is used throuout the program. Now, when I compile, I get 6 errors, all of them "Use of possibly unassigned field 'awayTime'" or "Use of possibly
unassigned field 'intlTime'". It is correct, it is possible that these
fields aren't assigned, but I don't care. It's inside of a struct, and
everything inside of a struct gets assigned its default value anyway.


Local variables *don't* have default values, according to the C# spec.
That's what you're running into.
This is difficult to explain, but if anyone else has had this problem and fixed it, i'd love to know how. Thanks.


The easiest way to fix it is to change:

MyStruct foo;

to

MyStruct foo = new MyStruct();

in your code.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

Nov 15 '05 #3
will post some sample code when I get home later today. Stay tuned!

Chris LaJoie

"Jon Skeet" <sk***@pobox.co m> wrote in message
news:MP******** *************** *@news.microsof t.com...
Chris LaJoie <ch***@etriptra der.com> wrote:
The struct var was being used inside of a foreach loop. Just for kicks (a hunch) I changed the foreach to a for, looping through the array. This
solved everything.


Interesting - could you post some sample code? (Just enough to show
what's going on.)
Simply using bla = new StructName() would not have worked in this case
(because the values were being read from, not assigned to).


I'm not sure I follow you, to be honest... if you're assuming that the
declaration gave you the default values, then assigning the default
value to it at the point of declaration should give you *exactly* the
same behaviour, but without the compile error.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

Nov 15 '05 #4
as I said earlier, my problem has been solved, but just to clear some things
up I'll post some sample code. I have my struct:

struct TestStruct {
public int a;
public int b;
}

now I have a function that only assigns the values of the struct. In my
case, this function did not get any compile errors:

public TestStruct[] Parse() {
TestStruct[] ret = new TestStruct[10];
for(int x = 0; x < ret.Length; x++) {
ret[x].a = 1;
ret[x].b = 2;
}
return ret;
}

as you can see, that function doesn't do any reading of the values, only
assigns them. I have another function, which reads the data and inserts it
in our database.

public bool InsertInDB(Test Struct[] things) {
StringBuilder sql = new StringBuilder(" INSERT....");
foreach(TestStr uct t in things) {
sql.Append(sqli fy(t.a) + ", "); // <-- compile error here
sql.Append(sqli fy(t.b) + ")"); // <-- compile error here

[...insert in db...etc...]
}
}

solving this was a matter of simply replacing the foreach with a for. I'm
not sure exactly what the difference is in the IL code generated, but
clearly there is one. here's how i fixed it:

public bool InsertInDB(Test Struct[] things) {
StringBuilder sql = new StringBuilder(" INSERT....");
for(int x = 0; x < things.Length; x++) {
sql.Append(sqli fy(things[x].a) + ", "); // <-- compile error here
sql.Append(sqli fy(things[x].b) + ")"); // <-- compile error here

[...insert in db...etc...]
}
}

I appologize for using such silly examples, but I'm not allowed to post
company code.
Chris LaJoie
"Jon Skeet" <sk***@pobox.co m> wrote in message
news:MP******** *************** *@news.microsof t.com...
Chris LaJoie <ch***@etriptra der.com> wrote:
The struct var was being used inside of a foreach loop. Just for kicks (a hunch) I changed the foreach to a for, looping through the array. This
solved everything.


Interesting - could you post some sample code? (Just enough to show
what's going on.)
Simply using bla = new StructName() would not have worked in this case
(because the values were being read from, not assigned to).


I'm not sure I follow you, to be honest... if you're assuming that the
declaration gave you the default values, then assigning the default
value to it at the point of declaration should give you *exactly* the
same behaviour, but without the compile error.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

Nov 15 '05 #5
Chris LaJoie <ch***@etriptra der.com> wrote:
as I said earlier, my problem has been solved, but just to clear some things
up I'll post some sample code. I have my struct:

struct TestStruct {
public int a;
public int b;
}

now I have a function that only assigns the values of the struct. In my
case, this function did not get any compile errors:

public TestStruct[] Parse() {
TestStruct[] ret = new TestStruct[10];
for(int x = 0; x < ret.Length; x++) {
ret[x].a = 1;
ret[x].b = 2;
}
return ret;
}
Right - just assigning will never have any problem.
as you can see, that function doesn't do any reading of the values, only
assigns them. I have another function, which reads the data and inserts it
in our database.

public bool InsertInDB(Test Struct[] things) {
StringBuilder sql = new StringBuilder(" INSERT....");
foreach(TestStr uct t in things) {
sql.Append(sqli fy(t.a) + ", "); // <-- compile error here
sql.Append(sqli fy(t.b) + ")"); // <-- compile error here

[...insert in db...etc...]
}
}
That *is* strange. I don't get a compile-time error with this, for
instance:

using System;

struct Foo
{
public int x;
}

class Test
{
static void Main(string[] args)
{
Foo[] f = new Foo[5];
f[0].x=5;
Bar (f);
}

static void Bar (Foo[] x)
{
foreach (Foo y in x)
{
Console.WriteLi ne (y.x);
}
}
}

<snip>
I appologize for using such silly examples, but I'm not allowed to post
company code.


That's not a problem at all - but I'm still finding it hard to see why
you're getting an error in the first place. Could you try compiling my
code above? It should compile without warning. If it does, could you
try constructing a similar complete test case which *doesn't* compile?

Which version of Visual Studio (or csc) are you using?

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
Nov 15 '05 #6
I'm using VS.NET 2003. If I tried to create an example program that didn't
compile, I wouldn't be able to. I honestly believe that this is a problem
with the C# compiler. These problems crop up in code that HAS worked for
months. Usually silly things like changing a foreach to a for will fix it.
For example, I fixed one a couple weeks ago. Only one member of the struct
was causing compile errors, so I changed the code around inside the struct.
Here's how I did it.

struct TestStruct {
public int a; // <-- still works fine
//public int b; // <-- broken
private int m_b;
public int b {
get {return m_b;}
set {m_b = value;}
}
}

that's right, simply changing a public variable to a property fixed the
problem.

I've researched the error (Use of possibly unassigned field) thoroughly.
Google only came up with documentation, not anyone else with problems.
Something I haven't tried is to compile it on another computer when it does
not compile on mine.

I do appreciate your interest in this, but I'm afraid that in the end we
won't be any closer to figuring it out.

Chris LaJoie

"Jon Skeet" <sk***@pobox.co m> wrote in message
news:MP******** *************** *@news.microsof t.com...
Chris LaJoie <ch***@etriptra der.com> wrote:
as I said earlier, my problem has been solved, but just to clear some things up I'll post some sample code. I have my struct:

struct TestStruct {
public int a;
public int b;
}

now I have a function that only assigns the values of the struct. In my
case, this function did not get any compile errors:

public TestStruct[] Parse() {
TestStruct[] ret = new TestStruct[10];
for(int x = 0; x < ret.Length; x++) {
ret[x].a = 1;
ret[x].b = 2;
}
return ret;
}


Right - just assigning will never have any problem.
as you can see, that function doesn't do any reading of the values, only
assigns them. I have another function, which reads the data and inserts it in our database.

public bool InsertInDB(Test Struct[] things) {
StringBuilder sql = new StringBuilder(" INSERT....");
foreach(TestStr uct t in things) {
sql.Append(sqli fy(t.a) + ", "); // <-- compile error here
sql.Append(sqli fy(t.b) + ")"); // <-- compile error here

[...insert in db...etc...]
}
}


That *is* strange. I don't get a compile-time error with this, for
instance:

using System;

struct Foo
{
public int x;
}

class Test
{
static void Main(string[] args)
{
Foo[] f = new Foo[5];
f[0].x=5;
Bar (f);
}

static void Bar (Foo[] x)
{
foreach (Foo y in x)
{
Console.WriteLi ne (y.x);
}
}
}

<snip>
I appologize for using such silly examples, but I'm not allowed to post
company code.


That's not a problem at all - but I'm still finding it hard to see why
you're getting an error in the first place. Could you try compiling my
code above? It should compile without warning. If it does, could you
try constructing a similar complete test case which *doesn't* compile?

Which version of Visual Studio (or csc) are you using?

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

Nov 15 '05 #7
Chris LaJoie <ch***@etriptra der.com> wrote:
I'm using VS.NET 2003. If I tried to create an example program that didn't
compile, I wouldn't be able to. I honestly believe that this is a problem
with the C# compiler.
Yes, it sounds like it. Certainly the code you posted looked like it
was fine.
These problems crop up in code that HAS worked for
months. Usually silly things like changing a foreach to a for will fix it.
For example, I fixed one a couple weeks ago. Only one member of the struct
was causing compile errors, so I changed the code around inside the struct.
<snip>

That sounds very strange.
Something I haven't tried is to compile it on another computer when it does
not compile on mine.
That's definitely worth doing. I can't imagine how your VS.NET
installation could be damaged in such a subtle way, but it's definitely
worth a try.
I do appreciate your interest in this, but I'm afraid that in the end we
won't be any closer to figuring it out.


You could well be right :(

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
Nov 15 '05 #8
One question I have it if you're using incremental compilation.

--
--Grant
This posting is provided "AS IS" with no warranties, and confers no rights.
Nov 15 '05 #9
No, none of my projects use incremental build.

Chris LaJoie

"Grant Richins [MS]" <gr*****@online .microsoft.com> wrote in message
news:e2******** ******@TK2MSFTN GP09.phx.gbl...
One question I have it if you're using incremental compilation.

--
--Grant
This posting is provided "AS IS" with no warranties, and confers no rights.

Nov 15 '05 #10

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