From b783cbb981a6bcdcd8d830db01465bc94cebd50e Mon Sep 17 00:00:00 2001
From: Ying-Li Niu <64801511@qq.com>
Date: Thu, 11 Jun 2026 19:11:34 +0800
Subject: [PATCH] =?UTF-8?q?fix(fortran):=20=E4=BF=AE=E5=A4=8D=20read=5Fcoo?=
 =?UTF-8?q?rd=20=E4=B8=AD=20line(0:0)=20=E5=AD=97=E7=AC=A6=E4=B8=B2?=
 =?UTF-8?q?=E8=B6=8A=E7=95=8C=E5=AF=BC=E8=87=B4=E5=B4=A9=E6=BA=83?=
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错误码 3221225785 (0xC0000005 = STATUS_ACCESS_VIOLATION) 由
read_coord 中列数统计的双重条件导致：
  line(i:i) /= ' ' .and. (i == 1 .or. line(i-1:i-1) == ' ')
Fortran 不保证 .or. 短路求值，当 i=1 时 line(0:0) 触发
内存越界。拆分为嵌套 if 块，确保只有在 i>1 时才访问
line(i-1:i-1)。
---
 engines/fortran/main.f90        | 8 +++++++-
 examples/case06/input/input.txt | 4 ++--
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/engines/fortran/main.f90 b/engines/fortran/main.f90
index 0dcaef4..c6c1f46 100644
--- a/engines/fortran/main.f90
+++ b/engines/fortran/main.f90
@@ -334,7 +334,13 @@ subroutine read_coord(input_dir, n_atoms, atom_ids, masses, radii, pos_0, vel_0,
     read(u, '(a)', iostat=ios) line
     ncols = 0
     do i = 1, len_trim(line)
-        if (line(i:i) /= ' ' .and. (i == 1 .or. line(i-1:i-1) == ' ')) ncols = ncols + 1
+        if (line(i:i) /= ' ') then
+            if (i == 1) then
+                ncols = ncols + 1
+            else if (line(i-1:i-1) == ' ') then
+                ncols = ncols + 1
+            end if
+        end if
     end do
 
     do
diff --git a/examples/case06/input/input.txt b/examples/case06/input/input.txt
index df99e09..a65582a 100644
--- a/examples/case06/input/input.txt
+++ b/examples/case06/input/input.txt
@@ -16,7 +16,7 @@ plot_wave_save_mp4: 1  # 输出波形 MP4（需 step_plot_wave=1）
 
 # ── 计算引擎 ──────────────────────────────────
 # 可选: python, c, cpp, fortran, java
-engine: python      # 默认使用 python 引擎
+engine: fortran      # 默认使用 python 引擎
 
 # ── 盒子 ──────────────────────────────────────
 box_a: 80.0         # 立方体半边长，粒子被限制在 [-box_a, box_a]³ 内
@@ -63,7 +63,7 @@ warmup_steps: 0           # 默认 0（立即开始记录）
 
 # 总模拟时间（秒），程序自动计算 NT = T_total / DT
 # 如果同时指定了 NT，以 NT 为准
-T_total:  4.0
+T_total:  10.0
 
 # 抽帧间隔（每 NSTEP 步取一帧用于动画）
 NSTEP: 100