There has been several years since I first learned c programming language. I use it to analysis data, simulate and create applications. But C is not good at these applications, instead, it's more popular in low level world, such as operating systems, and embedded systems. To write code for embedded system, one need more advanced c knowledges. While that is something you teachers will not teach you.
All data structure are implemented with c MACROs. You will find them similar with the source code of linux or freebsd. Yes.
Sometimes we need to change parameters to run the program, but it's stupid to compile the code every time you need to make changes. Some would type the perameters to programs when running with scanf or getc. But there is a more convinent way for us to choose. There exists a special data in c programs, it's argc and argv. That's a method to pass string to you program once you run your programs. But it requires some special modifications on the declearation of main function.
#int main(int argc, char **argv)All the strings you type when run the program through command line will be stored in argv, note that argv[0] stores the program name. And argc is the length of argv parameter array. To read parameters in a elegant way, we can use the libs of get_opt(), and get_opt_loog().
It's not easy if you need to modify many parameters at startup. To solve this problem, one can write the arguments with their vallues into a file, and read this file at startup, to load the settings. In the folder, there is a simple implement of config read header. For details, see the source codes, which are easy to understand.
Sometimes we have many different ways to solve a problem, but don't know which function we will use. We want the user to choose it. A convinent way is to use pointer to functions, you just change the pointer. But use the pointer directly will make the code messy. We can use a method called 'call_back' function. The idea if that, you can just pass the pointer to a function, and the pointer of input structure and output pointers (usually no output). This function is just a 'method' to this problem.
It's an important concept in advanced c programming. With this feature, your program can behave like a system. Because you can expand your "System" by load new modules. The program can then become more and more complete (without restart, recompile, and so on). It's very important especially for embadded system. Users may want to modify the functions, or behaviors of system without restart.
- gcc main.c
compile and link automatically. But stupid.
> gcc main.c
> ls
a.out main.c- gcc main.c -o main
compile and link, set the output manually.
> gcc main.c -o main
> ls
main main.c- gcc -c file.c
compile but not link.
> gcc -c file.c
> ls
file.c file.o-
gcc -D
D is related to Macro, you can define preprocess macros when compile -
gcc -fPIC & gcc -fpic
PIC generates position independent code (PIC) for shared libraries, while pic generates more efficient code, if supported by the platform compiler. -
gcc -Wall
show all warning messages -
gcc -g
generates debug information to be used by GDB debugger. -
gcc -O#
set the optimize type
| Optimize level | description | exec time | code size | mem usage | compile time |
|---|---|---|---|---|---|
| O0 | optimization for compilation time (default) | + | + | - | - |
| O1 | optimization for code size and execution time | - | - | + | + |
| O2 | optimization more for code size and execution time | -- | + | ++ | |
| O3 | optimization more for code size and execution time | --- | + | +++ | |
| Os | optimization for code size | -- | ++ | ||
| Ofast | O3 with fast none accurate math calculations | --- | + | +++ |