Table of Contents

• 1. rcheck
  • 1.1. Syntax
  • 1.2. Stack Effects
  • 1.3. Description
  • 1.4. PostScript Level
  • 1.5. Examples
  • 1.6. Common Use Cases
    • 1.6.1. Safe Access
    • 1.6.2. Validation
    • 1.6.3. Permission Checking
  • 1.7. Common Pitfalls
  • 1.8. Error Conditions
  • 1.9. Access Attributes
  • 1.10. Implementation Notes
  • 1.11. See Also

1. rcheck

Tests whether an object’s access attribute permits reading its value.

1.1. Syntax

array rcheck → bool
packedarray rcheck → bool
dict rcheck → bool
file rcheck → bool
string rcheck → bool

1.2. Stack Effects

Table 1. Before

Level	Object
0	Composite object

Table 2. After

Level	Object
0	bool (true if readable, false otherwise)

1.3. Description

rcheck tests whether the operand’s access attribute permits its value to be read explicitly by PostScript operators.

Returns: * true if access is unlimited or readonly * false if access is executeonly or noaccess

1.4. PostScript Level

Level 1 and later

1.5. Examples

Readable objects

[1 2 3] rcheck          % true (unlimited)
(text) readonly rcheck  % true (readonly)

Non-readable objects

{ code } executeonly rcheck  % false
{ code } noaccess rcheck     % false

File objects

(file.ps) (r) file rcheck  % true (read mode)
(file.ps) (w) file rcheck  % false (write mode)

1.6. Common Use Cases

1.6.1. Safe Access

/safe-get {
  2 copy rcheck {
    get
  } {
    pop pop null
  } ifelse
} def

1.6.2. Validation

/validate-readable {
  dup rcheck not {
    /invalidaccess cvx exec
  } if
} def

1.6.3. Permission Checking

dict rcheck {
  % Can read dictionary
  dict { pop = } forall
} {
  % Cannot read
  (Dictionary not readable) print
} ifelse

1.7. Common Pitfalls

Execute-Only ≠ No Read - Execute-only objects cannot be read but can be executed.

{ 1 2 add } executeonly
dup rcheck         % false (cannot read)
dup exec           % Works! (can execute)

Confusing rcheck with xcheck - rcheck tests read access, xcheck tests executable attribute.

Check Before Reading - Use rcheck before operations that read object values.

1.8. Error Conditions

Error	Condition
[stackunderflow]	No operand on stack
[typecheck]	Operand not a composite object or file

1.9. Access Attributes

Attribute	Can Read?	Can Write?	Can Execute?
Unlimited	Yes	Yes	Yes
Readonly	Yes	No	Yes
Executeonly	No	No	Yes
Noaccess	No	No	No

1.10. Implementation Notes

• Fast operation (checks access bits)

• Does not modify the object

• Works only on composite objects and files

• Simple objects (numbers, booleans) have no access attribute

1.11. See Also

• wcheck - Test if writable

• xcheck - Test if executable

• Access operators: readonly, executeonly, noaccess

• type - Get object type