文件系统完结

C13-Linux系统编程/C13-Linux系统编程学习笔记.md

@@ -895,11 +895,77 @@ int getopt_long(int argc, char *const argv[], const char *optstring,
 ```
 
 ### 环境变量
+**KEY = VALVE**
+可以通过`export`命令查看
+
+```c
+char *getenv(const char *name);
+
+/*
+ * change or add
+ * 
+ * @prarm: overwrite  是否覆盖
+ *
+ * 覆盖时是释放原来的空间，重新分配
+ */
+int setenv(const char *name, const char *value, int overwrite);
+int unsetenv(const char *name);
+
+/*
+ * 和getenv一样的作用，change or add
+ * 用法不一样，且没有const修饰
+ */
+int putenv(char *string);
+```
 
 ### C程序的存储空间布局
+`pmap`命令，查看进程空间布局
 
 ### 库
+- 动态库
+- 静态库
+- 手工装载库
+    ```c
+    void *dlopen(const char *filename, int flag);
+    char *dlerror(void);
+    int dlclose(void *handle);
+    void *dlsym(void *handle, const char *symbol);
+    // Link with -ldl
+    ```
 
 ### 函数之间正常的跳转
+`goto`无法跨函数跳转。
+
+```c
+/*
+ *  设置跳转点
+ *  
+ * @return  0  说明是在设置跳转点
+ * @return 非0 说明是通过 longjmp 返回
+ */
+int setjmp(jmp_buf env);
+
+/*
+ * 跳转到跳转点
+ *
+ * @prarm: env  跳转点 
+ * @prarm: val  传递给 setjmp 的值
+ */
+void longjmp(jmp_buf env, int val);
+```
 
 ### 资源的获取及控制
+`ulimit -a`
+
+```c
+// get/set resource limits
+int getrlimit(int resource, struct rlimit *rlim);
+int setrlimit(int resource, const struct rlimit *rlim);
+
+// 普通用户不能设置超过硬限制
+// root 用户可以 升高/降低 硬限制
+struct rlimit {
+    rlim_t rlim_cur;  /* soft limit */
+    rlim_t rlim_max;  /* hard limit */
+};
+```

C13-Linux系统编程/fs/getenv.c

@@ -0,0 +1,17 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+int main(int argc, char **argv)
+{
+
+    puts(getenv("PATH"));
+
+    getchar();
+    /**
+     *  ./getenv
+     *  ps axf | grep getenv
+     *  pmap 4938
+     */
+
+    exit(0);
+}

C13-Linux系统编程/fs/jmp.c

@@ -0,0 +1,99 @@
+#include <setjmp.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+static jmp_buf save;
+
+static void d(void)
+{
+    printf("%s():Begin.\n", __FUNCTION__);
+
+    printf("%s():Jump now.\n", __FUNCTION__);
+    longjmp(save, 6);
+    // longjmp(save, 0);   // !!! 如果返回0，实际会返回1，避免与另一种情况冲突
+
+    printf("%s():End.\n", __FUNCTION__);
+}
+
+static void c(void)
+{
+    printf("%s():Begin.\n", __FUNCTION__);
+    printf("%s():Call d().\n", __FUNCTION__);
+
+    d();
+
+    printf("%s():d() returned.\n", __FUNCTION__);
+    printf("%s():End.\n", __FUNCTION__);
+}
+
+static void b(void)
+{
+    printf("%s():Begin.\n", __FUNCTION__);
+    printf("%s():Call c().\n", __FUNCTION__);
+
+    c();
+
+    printf("%s():c() returned.\n", __FUNCTION__);
+    printf("%s():End.\n", __FUNCTION__);
+}
+
+static void a(void)
+{
+    int ret;
+
+    printf("%s():Begin.\n", __FUNCTION__);
+
+    ret = setjmp(save);
+    if (0 == ret)
+    {
+        printf("%s():Call b().\n", __FUNCTION__);
+        b();
+        printf("%s():b() returned.\n", __FUNCTION__);
+    }
+    else
+    {
+        printf("%s():Jumped back here with code %d.\n", __FUNCTION__, ret);
+    }
+
+    printf("%s():End.\n", __FUNCTION__);
+}
+
+
+/**
+ * @brief   jmp
+ * @details
+ *           d跳回a
+ *
+ * @param    argc
+ * @param    argv
+ * @return  int
+ */
+int main(int argc, char **argv)
+{
+    printf("%s():Begin.\n", __FUNCTION__);
+    printf("%s():Call a().\n", __FUNCTION__);
+
+    a();
+
+    printf("%s():a() returned.\n", __FUNCTION__);
+    printf("%s():End.\n", __FUNCTION__);
+
+    exit(0);
+}
+
+
+// ! out
+// main():Begin.
+// main():Call a().
+// a():Begin.
+// a():Call b().
+// b():Begin.
+// b():Call c().
+// c():Begin.
+// c():Call d().
+// d():Begin.
+// d():Jump now.
+// a():Jumped back here with code 6.
+// a():End.
+// main():a() returned.
+// main():End.

C13-Linux系统编程/fs/myenv.c

@@ -0,0 +1,13 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+extern char **environ;
+
+int main(int argc, char **argv)
+{
+
+    for (int i = 0; environ[i] != NULL; i++)
+        puts(environ[i]);
+
+    exit(0);
+}