{"record":{"id":"9aefb298e771809a","repo":"java-native-access/jna","slug":"invalid-structure-field-in-getclass-field-name-structfield","errorCode":null,"errorMessage":"Invalid Structure field in \" + getClass() + \", field name '\" + structField.name + \"' (\" + structField.type + \"): \" + e.getMessage()","messagePattern":"Invalid Structure field in \" \\+ getClass\\(\\) \\+ \", field name '\" \\+ structField\\.name \\+ \"' \\(\" \\+ structField\\.type \\+ \"\\): \" \\+ e\\.getMessage\\(\\)","errorType":"exception","errorClass":"IllegalArgumentException","httpStatus":null,"severity":"error","filePath":"src/com/sun/jna/Structure.java","lineNumber":1437,"sourceCode":"                    throw new IllegalArgumentException(msg);\n                }\n            }\n\n            if (value == null) {\n                value = initializeField(structField.field, type);\n            }\n\n            try {\n                structField.size = getNativeSize(nativeType, value);\n                fieldAlignment = getNativeAlignment(nativeType, value, firstField);\n            }\n            catch(IllegalArgumentException e) {\n                // Might simply not yet have a type mapper set yet\n                if (!force && typeMapper == null) {\n                    return null;\n                }\n                String msg = \"Invalid Structure field in \" + getClass() + \", field name '\" + structField.name + \"' (\" + structField.type + \"): \" + e.getMessage();\n                throw new IllegalArgumentException(msg, e);\n            }\n\n            // Align fields as appropriate\n            if (fieldAlignment == 0) {\n                throw new Error(\"Field alignment is zero for field '\" + structField.name + \"' within \" + getClass());\n            }\n            info.alignment = Math.max(info.alignment, fieldAlignment);\n            if ((calculatedSize % fieldAlignment) != 0) {\n                calculatedSize += fieldAlignment - (calculatedSize % fieldAlignment);\n            }\n            if (this instanceof Union) {\n                structField.offset = 0;\n                calculatedSize = Math.max(calculatedSize, structField.size);\n            }\n            else {\n                structField.offset = calculatedSize;\n                calculatedSize += structField.size;\n            }","sourceCodeStart":1419,"sourceCodeEnd":1455,"githubUrl":"https://github.com/java-native-access/jna/blob/d036ad9781adad4b66693e8fa7098e4ac665e0a3/src/com/sun/jna/Structure.java#L1419-L1455","documentation":"While computing the layout with force=true, a field's native size lookup failed (IllegalArgumentException from getNativeSize). If a TypeMapper is configured (or force is set) JNA cannot silently defer, so it rethrows as IllegalArgumentException with the Structure class, field name and type. It means a field type still has no valid native mapping.","triggerScenarios":"calculateSize(true)/size(true) or write paths where a field type has no native size even after type mapper consideration; typeMapper != null but the mapper does not handle the offending type; validation triggered with force on an incompletely-defined structure.","commonSituations":"TypeMapper registered but missing converters for some field types; nested structures that fail their own validation; using force during tests to surface layout problems early.","solutions":["Fix the underlying field type mapping (see the cause message's type) with a supported type or a TypeMapper/NativeMapped","Ensure the TypeMapper handles every field type on both to/from sides","Avoid forcing size calculation until all fields are properly initialized and mapped","Inspect the cause chain (msg, e) to identify the exact failing type"],"exampleFix":"// before\nmapper lacks converter for CustomType; field: public CustomType x;\n// after\n// add to mapper:\ngetToNativeConverter(CustomType.class) / getFromNativeConverter(CustomType.class)\n// or make CustomType implement NativeMapped","handlingStrategy":"validation","validationCode":"for (Field f : S.class.getFields()) {\n    try {\n        // ensure each field type is sizeable before forcing layout\n        if (typeMapper != null && typeMapper.getToNativeConverter(f.getType()) == null\n            && !NativeMapped.class.isAssignableFrom(f.getType())) {\n            throw new IllegalStateException(\"No size mapping for \" + f);\n        }\n    } catch (IllegalArgumentException e) { throw new IllegalStateException(f + \" unmapped\", e); }\n}","typeGuard":null,"tryCatchPattern":"try {\n    s.size();\n} catch (IllegalArgumentException e) {\n    if (e.getMessage() != null && e.getMessage().contains(\"Invalid Structure field\")) {\n        // inspect e.getCause() to find the unmapped type and fix the mapper\n        throw new IllegalStateException(\"Fix field mapping: \" + e.getMessage(), e.getCause());\n    }\n    throw e;\n}","preventionTips":["Ensure TypeMapper covers all field types before using force=true","Prefer lazy size calculation over forced validation on incomplete structures","Keep NativeMapped implementations complete (nativeSize/toNative/fromNative)","Test structure layout immediately after adding fields"],"tags":["jna","structure","native-size","type-mapper"],"backgroundTag":"type-mismatch","analyzedSha":"d036ad9781adad4b66693e8fa7098e4ac665e0a3","analyzedAt":"2026-09-12T06:50:59.239Z","contentChangedAt":"2026-09-12T06:50:59.239Z","schemaVersion":2},"datasetVersion":"2026-09-14T05:17:10.506Z"}