{"record":{"id":"aa0364eb1a88c2ab","repo":"java-native-access/jna","slug":"no-such-field-name","errorCode":null,"errorMessage":"No such field: \" + name","messagePattern":"No such field: \" \\+ name","errorType":"exception","errorClass":"IllegalArgumentException","httpStatus":null,"severity":"error","filePath":"src/com/sun/jna/Structure.java","lineNumber":628,"sourceCode":"            }\n        }\n        finally {\n            busy().remove(this);\n            if (this instanceof Structure.ByReference && reading().get(getPointer()) == this) {\n                reading().remove(getPointer());\n            }\n        }\n    }\n\n    /** Returns the calculated offset of the given field.\n     * @param name field to examine\n     * @return return offset of the given field\n     */\n    protected int fieldOffset(String name) {\n        ensureAllocated();\n        StructField f = fields().get(name);\n        if (f == null) {\n            throw new IllegalArgumentException(\"No such field: \" + name);\n        }\n        return f.offset;\n    }\n\n    /** Force a read of the given field from native memory.  The Java field\n     * will be updated from the current contents of native memory.\n     * @param name field to be read\n     * @return the new field value, after updating\n     * @throws IllegalArgumentException if no field exists with the given name\n     */\n    public Object readField(String name) {\n        ensureAllocated();\n        StructField f = fields().get(name);\n        if (f == null)\n            throw new IllegalArgumentException(\"No such field: \" + name);\n        return readField(f);\n    }\n","sourceCodeStart":610,"sourceCodeEnd":646,"githubUrl":"https://github.com/java-native-access/jna/blob/d036ad9781adad4b66693e8fa7098e4ac665e0a3/src/com/sun/jna/Structure.java#L610-L646","documentation":"Structure.fieldOffset(String) throws this IllegalArgumentException when the requested name is not a mapped field of the structure. fields() only contains JNA-mapped public instance fields, so any typo or non-mapped member lookup fails after ensureAllocated() runs.","triggerScenarios":"Calling structure.fieldOffset(\"fieldName\") with a name that does not exactly match a mapped public field — typos, wrong case, private/protected/static fields, transient fields, or fields of unsupported types that JNA skipped during layout.","commonSituations":"Hand-writing native offset tables from Java structs; renaming a Java field without updating fieldOffset callers; assuming inherited or private fields participate in the layout.","solutions":["Correct the field name to exactly match the declared public field (case-sensitive).","Make the field public, non-static, non-transient and of a JNA-supported type so it is mapped and gets an offset.","Programmatically list valid names first (structure.getFields() / fields().keySet()) to find the right spelling.","If the offset of an unmapped member is needed, wrap it in a supported JNA type or compute it manually outside fieldOffset."],"exampleFix":"// before\nclass Point extends Structure {\n    public int x;\n    public int y;\n}\nint off = new Point().fieldOffset(\"X\"); // IllegalArgumentException: No such field: X\n\n// after\nint off = new Point().fieldOffset(\"x\");","handlingStrategy":"validation","validationCode":"Set<String> names = structure.getFields().stream().map(Field::getName).collect(Collectors.toSet());\nif (!names.contains(name)) {\n    throw new IllegalArgumentException(name + \" is not a mapped field; valid: \" + names);\n}","typeGuard":"static boolean hasField(Structure s, String name) {\n    return s.getFields().stream().anyMatch(f -> f.getName().equals(name));\n}","tryCatchPattern":"try {\n    int off = structure.fieldOffset(name);\n} catch (IllegalArgumentException e) {\n    // name is not a mapped public field; list valid names for diagnosis\n    throw new IllegalArgumentException(\"valid fields: \" + structure.getFields(), e);\n}","preventionTips":["Match field names exactly and case-sensitively; prefer referencing Field constants or the getter method name.","Only public, non-static, non-transient fields of supported JNA types are mapped and addressable.","Generate offset lookups from the Structure class definition rather than free-typed strings."],"tags":["jna","structure","field-lookup","invalid-argument"],"backgroundTag":"resource-not-found","analyzedSha":"d036ad9781adad4b66693e8fa7098e4ac665e0a3","analyzedAt":"2026-09-12T06:50:59.239Z","contentChangedAt":"2026-09-12T06:50:59.239Z","schemaVersion":2},"datasetVersion":"2026-09-19T12:17:13.211Z"}