What are sequence points in C? The comp.lang.c FAQ explains this quite well. A sequence point is a point in time at which the dust has settled and all side effects which have been seen so far are guaranteed to be complete. The sequence points listed in the C standard are: at the end of […]
Posts tagged C
59 posts in total.
How to make ctags recognize specific files with certain extensions as C source files?
How to make ctags recognize specific files with certain extensions such as .c0 or .puc as C source files? You may add this line to your ~/.ctags: –langmap=c:+.c0,c:+.puc Answered by Eric Z Ma.
How to make taglist recognize specific files with certain extensions as C source files?
How to make taglist recognize specific files with certain extensions as C source files? You may try adding this line to your ~/.vimrc: autocmd BufRead,BufNewFile *.c0 set filetype=c Reference: https://stackoverflow.com/questions/9013263/vim-tagslist-plugin-not-detecting-custom-language-racket Answered by Eric Z Ma.
How to get the time at millisecond level on Linux with command line?
I know that gettimeofday() is a nice API. But how to get the number of seconds with milliseconds since the epoch time? You can get the time at nano-seconds level (although it is not guaranteed that the last digits are accurate) by: date +%s.%N Answered by Eric Z Ma.
How to get the file length in C on Linux
How to get the file length in C on Linux given the address of the file (e.g. “/tmp/a.txt”)? This function returns the length of the file: #include <sys/stat.h> long file_length(char *f) { struct stat st; stat(f, &st); return st.st_size; } Answered by Eric Z Ma.
How to catch the kill signals sent by kill in C on Linux?
How to catch the kill signals sent by the kill command in C programs on Linux? For example, I have a daemon progd running, and will kill it by: pkill progd The question is how to catch the signal sent by the kill command and response to it in the progd program implemented in C […]
How to get the directory path and file name from a absolute path in C on Linux
How to get the directory path and file name from a absolute path in C on Linux? For example, with “/foo/bar/baz.txt”, it will produce: “/foo/bar/” and “baz.txt”. You can use the APIs basename and dirname to parse the file name and directory name. A piece of C code: #include <libgen.h> #include <string.h> char* local_file = […]
RAII equivalent idiom in C for error handling
RAII is great for error handling in C++. Is there any equivalent idiom in C? Please check the discussion in this post https://www.systutorials.com/5311/raii-like-error-handling-and-resource-management-in-c/ which discussed how to organize the C code to provide RAII-like semantics. Answered by Eric Z Ma.
How to make a static library (.a) on Linux
How to make a static library (.a) on Linux? How to generate a library from C programs in files lib1.c and lib2.c: $ gcc -c lib1.c lib2.c Create a library “libmy.a” using ar: $ ar -cvq libmy.a lib1.o lib2.o You can also list the files in a library with ar: $ ar -t libmy.a You […]
How to set and get an environment variable in C on Linux?
How to set and get an environment variable in C on Linux? You can use the setenv and getenv POSIX APIs to set and get environment variables. To add or change environment variable: #include <stdlib.h> int setenv(const char *envname, const char *envval, int overwrite); To get value of an environment variable: #include <stdlib.h> char *getenv(const […]
C++ cout formatting output
How to format outputs with cout in C++? You need IO Manipulators <iomanip>: Header providing parametric manipulators. There are also good tutorials on the Web: Output Formatting: http://arachnoid.com/cpptutor/student3.html Formatting Cout Output in C++ using iomanip: http://www.cprogramming.com/tutorial/iomanip.html Answered by anonymous.
g++: sorry, unimplemented: non-trivial designated initializers not supported
g++ (version g++ (GCC) 4.8.1 20130603 (Red Hat 4.8.1-1)) report: $ g++ -std=c++11 solution.cpp -o sol solution.cpp: In function ‘int main()’: solution.cpp:50:57: sorry, unimplemented: non-trivial designated initializers not supported Stat init_stat {.depth = 0, .moves = tv, .vec = init}; ^ solution.cpp:50:57: sorry, unimplemented: non-trivial designated initializers not supported solution.cpp:50:57: sorry, unimplemented: non-trivial designated initializers […]
Is cin much slower than scanf in C++?
I frequently hear that cin is significantly slower than scanf in C++. Is this true? And how to improve the efficiency of cin? It is really nice to use most of time. One discussion about that cin is very slow is here: http://apps.topcoder.com/forums/?module=Thread&threadID=508058&start=0&mc=7 Answered by anonymous. In short: cin is not always slower (can be […]
How to call C functions from OCaml code
I am writing a OCaml program but want to call some C functions provided in some source code or library. How to achieve this? Is there any good tutorials on this? A very good tutorial that is easy to follow and understand: How to wrap C functions to OCaml. A comprehensive reference manual: Chapter 19 […]
How to statically link C and C++ programs
How to statically compile C and C++ projects? The compiled executable should lead no dynamical library during execution. I use gcc/g++ to compile the projects. Check this post: https://www.systutorials.com/5217/how-to-statically-link-c-and-c-programs-on-linux-with-gcc/ Answered by anonymous.
x86-64 calling convention by gcc
What is the x86-64 calling convention by gcc? The calling convention of the System V AMD64 ABI is followed on GNU/Linux. The registers RDI, RSI, RDX, RCX, R8, and R9 are used for integer and memory address arguments and XMM0, XMM1, XMM2, XMM3, XMM4, XMM5, XMM6 and XMM7 are used for floating point arguments. For […]
strcmp and strncmp implementation in glibc
What is the strcmp and strncmp implementation in glibc? strcmp implementation in glibc 2.16: string/strcmp.c /* Copyright (C) 1991, 1996, 1997, 2003 Free Software Foundation, Inc. This file is part of the GNU C Library. The GNU C Library is free software; you can redistribute it and/or modify it under the terms of the GNU […]
How to get the size of a file in C
How to get a file’s size in C? If you have the file stream (FILE * f): fseek(f, 0, SEEK_END); // seek to end of file size = ftell(f); // get current file pointer fseek(f, 0, SEEK_SET); // seek back to beginning of file // proceed with allocating memory and reading the file Or, #include […]
scanf is dangerous, but what is the reason?
We all know scanf / fscanf / sscanf is dangerous. But why? what is the exact reason? I thought the ‘%s’ is a problem that causes buffer overflow and ‘fgets’ is a better solution. But is it the exact reason? I pased a discussion by AndreyT and his discussion helps me figure it out: Claiming […]
C: converting string to long
How to convert a string to long in C? Use strtol or strtoul C library: strtol man page.strtoul man page. If the value of base is 0, the expected form of the subject sequence is that of a decimal constant, octal constant, or hexadecimal constant, any of which may be preceded by a ‘+’ or […]