Can't read bytes in data section

[MachineCode]

Can someone explain to me why this doesn't work, when it used to in an older version of PureBasic? The error message given is "Read data error: no more data" but I'm not trying to read more data than exists. WTF?

The manual states that the "byte" data type holds values from -128 to +127, and "word" from -32768 to +32767, but if I use anything less than "long" type, the loop doesn't read all the values. I don't understand why, as all the values in the data section are under +127.

Code: Select all

For num=1 To 15
  Read value.b
  Debug value
Next

DataSection
  Data.b 77,101,114,114,121,32,67,104,114,105,115,116,109,97,115
EndDataSection

[Comtois]

since 4.30

- Changed: 'Read' keyword now requiers a type (Read.l, Read.q etc.) to avoid 64 bits migration problems

Code: Select all

For num=1 To 15
  Read.b value.b
  Debug value
Next

DataSection
  Data.b 77,101,114,114,121,32,67,104,114,105,115,116,109,97,115
EndDataSection

[MachineCode]

Thanks for that. The manual needs updating, then. Because for the "Read" keyword, it currently shows [ and ] brackets, which means specifying a type is optional, and it says the default type (integer) is used if not specified. See:

Code: Select all

Read[.<type>] <variable>
The type of data to read is determined by the type suffix. The default type will be used if it is not specified.

[ts-soft]

The manual is correct, see:

Code: Select all

For num=1 To 4
  Read value.b
  Debug value
Next

DataSection
  Data.b 77,101,114,114,121,32,67,104,114,105,115,116,109,97,115
EndDataSection 

Reads all values as long in x86

[tinman]

Thanks for that. The manual needs updating, then. Because for the "Read" keyword, it currently shows [ and ] brackets, which means specifying a type is optional, and it says the default type (integer) is used if not specified. See:

Code: Select all

Read[.<type>] <variable>
The type of data to read is determined by the type suffix. The default type will be used if it is not specified.

Without the type specifier it reads an integer from memory, converts the integer to your byte variable and then increments by the number of bytes in an integer. Increasing by 4 or 8 bytes each time eventually runs off the end of your data section.

So as far as the syntax of the command is concerned the type is optional and the manual is currently syntactically correct, which is maybe misleading or unclear especially when the behaviour used to be different. If a change it required it would be required to the command, not just the manual.

Think about it in terms of peeking. The size of memory being read from depends on the command, not where the result is stored. You wouldn't do this and expect only a byte to be accessed in memory:

value.b = PeekI(?label)

So consider the Read command in the same way, you need to tell it what size to read using the suffix or it will default to integer. Perhaps the best option would be to make the type specifier mandatory (for example, you do not get a Peek command with an optional type).

[Fred]

Mandatory type looks like a good idea to avoid such trap.

[rsts]

Mandatory type looks like a good idea to avoid such trap.

Will this break existing code without a specified type?

If so, maybe just a clarification in the documentation?

[Fred]

It will probably break, but actually a code without suffix will break on 64 bit (as the default type will change). I don't think it's a reliable solution for the future (if i miss something, don't hesitate to tell).

[MachineCode]

It will probably break

Don't worry about that... it's just a simple search/replace to fix our sources. Go for it!