原创 What is the type of a constant in C? (U, UL, ULL, L, F)
Copied from here. When we write expressions like this in C: bool b = 1234567890 > 09876; What are the types of those
2020-06-26 21:04:49
原创 ud2: illegal opcode, Undefined Instruction
Following is xv6 (rev11) chapter2 exercise 5, Modify xv6 so that when a user program dereferences a null pointer,
2020-06-26 21:04:49
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原创 multithread: why main thread exit leads to other threads exit?
In linux multithread program, when main thread exit, other threads will exit too, why? How to keep other thread running
2020-06-26 21:04:49
原创 memory cache 直接映射、全相聯映射和組相聯映射
cpu的執行速度很快，cpu從memory讀取數據速度很慢，導致cpu需要等memory，爲了提高cpu的效率，根據程序的局部性原理(現在訪問的數據很有可能以後還會訪問)，引入了讀寫比較快的memory cache，cache用來存放剛剛
2020-06-26 21:04:49
原创 The Buddy System Algorithm
目錄 1. Why need the Buddy System Algorithm 2. What's the Buddy System Algorithm 2.1 how to find buddy 3. Code implementa
2020-06-26 21:04:49
原创 switch_to() in schedule()
Reading ULK about switch_to(prev, next, last), it's quite hard to understand why the need for the 3rd argument. It turn
2020-06-26 21:04:49
原创 pass flags to make implicit rules
The built-in implicit rules use several variables in their recipes so that, by changing the values of the variables, yo
2020-06-26 21:04:49
原创 程序輸出
1. copy from blog main() { int a[5]={1,2,3,4,5}; int *ptr=(int *)(&a+1); printf("%d,%d",*(a+1),*(ptr-1)); } 輸
2020-06-26 21:04:49
原创 Type conversions
All come from section 2.7 of the c programming language 2nd edition. BTW, this book is highly recommended for learning
2020-06-26 21:04:49
原创 thread: detached state
與其被稱爲state，可能稱爲flag更合適些，因爲detached state並不是thread生命週期中的一個state(例如，running)，而是一個flag，用來告訴OS當thread退出的時候，是否需要回收thread的res
2020-06-26 21:04:49
原创 why not 'switch case' accept float point in condition?
A switch case example as below. The expression used in switch must be integral type ( int, char and enum). Any other ty
2020-06-26 21:04:49
原创 malloc(0) & free(NULL)
man malloc / man free The malloc() function allocates size bytes and returns a pointer to the allocated memory. The
2020-06-26 21:04:49
原创 c sort function in library: qsort()
目錄 qsort() in C library example reference qsort() in C library Usually sort is the first step for an algorithm. In C, t
2020-06-26 21:04:49
原创 static variableS with same name
1. 多個c文件，每個文件都包含static int a; 2. 一個c文件中，有一個全局static int a;，在某個函數中，也有一個相同定義static int a; 這兩種情況都是合法的，另外這些變量a都是存放在同一個data段
2020-06-26 21:04:49
原创 c struct bitfield (結構體位域)
兩篇非常棒的文章。 1. 再談c語言位域 2. Section bitfields 簡要總結一下： C99 guarentees that bit-fields will be packed as tightly as possible,
2020-06-26 21:04:49