# 27-validation-halfwidth: Half-Width Character Validation

## 电信业务场景

电话号码格式校验。检查电话号码字段是否全为半角数字(0-9)，检测全角字符混入和长度超出。

## Description

Reads FILE-IN and validates that each character in IN-TEXT is
half-width (ASCII printable: X'20'-X'7E'). Validates length
constraints: 20 or fewer half-width characters pass; more than 20
is an error. Full-width characters or control characters cause
rejection.

## Validation Rules

| Rule                              | Result       | Error Code |
|-----------------------------------|--------------|------------|
| All characters X'20'-X'7E', <= 20 | PASS to GOOD | -          |
| Contains non-half-width character | FAIL to BAD | 01         |
| All half-width but >20 chars      | FAIL to BAD | 02         |

## Record Layout

### Input / Good Output (30 bytes)

| Field  | Type     | Length | Description |
|--------|----------|--------|-------------|
| TEXT   | PIC X    | 30     | Text to validate |

### Bad Output (32 bytes)

| Field    | Type     | Length | Description    |
|----------|----------|--------|----------------|
| TEXT     | PIC X    | 30     | Original text  |
| ERR-CODE | PIC X    | 2      | Error code     |

## Files

| File                          | Purpose                        |
|-------------------------------|--------------------------------|
| main-27-validation-halfwidth.cbl | Main COBOL program          |
| data-gen.sh                   | Generate test data             |
| run.sh                        | Compile, run, verify           |
| README.md                     | This file                      |

## Tests

| Test Case                        | Expected                    |
|----------------------------------|-----------------------------|
| 4 half-width chars               | PASS to GOOD                |
| 10 half-width chars              | PASS to GOOD                |
| 20 half-width chars (boundary)   | PASS to GOOD                |
| 25 half-width chars (too long)   | FAIL err 02                 |
| Mixed with full-width            | FAIL err 01                 |
| Full-width only                  | FAIL err 01                 |
| Half-width + control char        | FAIL err 01                 |
| All spaces (empty)               | PASS to GOOD                |

## Usage

```bash
cd 27-validation-halfwidth
bash data-gen.sh
bash run.sh
```

## Expected Behavior

- Half-width check uses byte comparison against X'20'-X'7E'.
- Full-width UTF-8 multi-byte characters have bytes > X'7E'
  and are detected as non-half-width.
- Length is computed by trimming trailing spaces.
- Only records meeting both conditions (half-width + <= 20 chars)
  are written to GOOD output.