f(void)
f() // can take any number of arguments
void Error(const char* format, ...)
{
va_list argptr;
va_start(argptr, format);
vfprintf(stderr, format, argptr);
va_end(argptr);
}
#define FOO abcd
#define MACRO1(FOO, x) FOO##_##x
// Won't work
#define MACRO2(x) MACRO1(FOO, x)
// This combination will
#define MACRO3(FOO, x) MACRO1(FOO, x)
#define MACRO4(x) MACRO3(FOO, x)
MACRO1(xyz, x) // xyz_x
MACRO2(jkl) // FOO_jkl
MACRO4(x) // abcd_x
# using if block as expression
# wrap compound expression in braces
# wrap that in parentheses
int i = ({int j; if (true) j = 1; else j = 2; j;});
https://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html
#include <pthread.h>
pthread_barrier_t barrier;
...
pthread_barrier_init(&barrier, NULL, nThreads);
...
pthread_barrier_wait(&barrier);
https://docs.oracle.com/cd/E19253-01/816-5137/gfwek/index.html
Pass -O0 as a flag to GCC.
https://stackoverflow.com/questions/5765899/how-to-disable-compiler-optimizations-in-gcc
#include <stdlib.h>
(double)rand() / RAND_MAX
https://stackoverflow.com/questions/33058848/generate-a-random-double-between-1-and-1
`gcc -print-prog-name=cpp` -v
https://stackoverflow.com/questions/344317/where-does-gcc-look-for-c-and-c-header-files
#include <filename> searches in implementation-dependent manner. Usually used to include standard library header files.
#include "filename" searches in the same directory as file containing include, and then does search that #include <filename> does.
@brief description should end with period. Add empty line between it and extended description to avoid having the extended description included in the brief.
Ignore file.
# configure in doxygen.conf
EXCLUDE = dir/ path/to/file.txt
https://stackoverflow.com/questions/34776315/doxygen-special-command-to-ignore-a-file
double NAN = 0.0/0.0;
double POS_INF = 1.0 /0.0;
double NEG_INF = -1.0/0.0;
https://stackoverflow.com/questions/1923837/how-to-use-nan-and-inf-in-c
Use strncpy or memcpy.
https://stackoverflow.com/questions/10530064/how-to-use-substring-function-in-c/10530098
#pragma GCC diagnostic ignored "-Wuninitialized"
foo(b); /* no diagnostic for this one */
#pragma GCC diagnostic pop
https://stackoverflow.com/questions/3378560/how-to-disable-gcc-warnings-for-a-few-lines-of-code
(void (*)(void *))SGENT_1_calc
// more readable alternative
typedef void sigrout_t(void*);
((sigrout_t*) SGENT_1_calc) (someptr);
https://stackoverflow.com/questions/15807333/cast-to-function-pointer
Used to suppress compiler warnings about unused variables.
int x;
(void) x;
https://stackoverflow.com/questions/34288844/what-does-casting-to-void-really-do
- struct member access, array subscripting (left-to-right)
- casting (right-to-left)
- +/- (addition) (left-to-right)
https://en.cppreference.com/w/c/language/operator_precedence
Compile using gcc -pthread ....
https://stackoverflow.com/questions/1662909/undefined-reference-to-pthread-create-in-linux
Unsigned overflow is defined by the C standard while signed overflow is not. Most likely because only one obvious unsigned representation while multiple signed representations.
Use pthread_cond_wait and pthread_cond_signal or pthread_cond_broadcast.
https://stackoverflow.com/questions/2085511/wait-and-notify-in-c-c-shared-memory
// multiple string literals are concatenated
char* my_str =
"Here is the first line."
"Here is the second line.";
https://jameshfisher.com/2016/11/30/c-multiline-literal/
Use strtok.
Note that strtok modifies the input string!
// strstr
char * source = "test string"; /* assume source address is */
/* 0x10 for example */
char * found = strstr( source, "in" ); /* should return 0x18 */
if (found != NULL) { /* strstr returns NULL if item not found */
int index = found - source; /* index is 8 */
/* source[8] gets you "i" */
}
// strchr
char *pos = strchr (myString, '#');
int pos = pos ? pos - myString : -1;
https://stackoverflow.com/questions/4824/string-indexof-function-in-c
strcat(s1, s2);
https://stackoverflow.com/questions/8465006/how-do-i-concatenate-two-strings-in-c/8465083
strncmp(pre, str, strlen(pre)) == 0
https://stackoverflow.com/questions/4770985/how-to-check-if-a-string-starts-with-another-string-in-c
strcmp(check, input) != 0
https://stackoverflow.com/questions/8004237/how-do-i-properly-compare-strings
#include <stdbool.h>
bool x = true;
printf("%d\n", x); // prints 1
https://stackoverflow.com/questions/17307275/what-is-the-printf-format-specifier-for-bool
Returns offset (in bytes) of element within a struct.
offsetof(my_struct, elem_in_struct)
https://en.wikipedia.org/wiki/Offsetof
Sign extend, then reinterpret.
https://stackoverflow.com/questions/19262851/what-is-the-rule-for-c-to-cast-between-short-and-int
Output and input operands are 0-indexed, starting with output operands and continuing with input operands.
int x = 1;
printf("%d\n", x);
asm("addl $1, %1"
: "=r" (x) // = means overwrites, r for register operand
: "ir" (x)); // i for integer operand, r for register operand
printf("%d\n", x);
int *y = &x;
printf("%d\n", *y);
asm("addl $1, (%0)"
:
: "ir" (y));
printf("%d\n", *y);
// This code copies src to dst and add 1 to dst.
int src = 1;
int dst;
asm ("mov %1, %0\n\t"
"add $1, %0"
: "=r" (dst)
: "r" (src));
printf("%d\n", dst);
// inline assembly to save %ds to variable
uint32_t x = 0;
asm("push %%ds; pop %0"
: "=r" (x)
:);
https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#Extended-Asm https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#OutputOperands https://gcc.gnu.org/onlinedocs/gcc/Simple-Constraints.html
asm("movl $0xffff000,4(%ebp)");
https://www.codeproject.com/Articles/15971/Using-Inline-Assembly-in-C-C https://www.ibiblio.org/gferg/ldp/GCC-Inline-Assembly-HOWTO.html
# generates foo.s
gcc -S foo.c
https://stackoverflow.com/questions/137038/how-do-you-get-assembler-output-from-c-c-source-in-gcc
static bool initialized = false;
__attribute__((constructor))
static void initialize(void) {
initialized = true;
// do some other initialization
}
int main(int argc, char **argv) {
// initialize will have been run before main started
return 0;
}
Only visible in the scope of the file it is define in.
static void staticFunc(void)
{
printf("Inside the static function staticFunc() ");
}
https://www.tutorialspoint.com/static-functions-in-c
Precision specifies minimum number of digits to be printed, zero-padded.
unsigned u = 0x40b8bu;
char arr[10];
sprintf(arr, "%.8x", u);
$ gcc test.c && ./a.out
0040b8bu
https://www.tutorialspoint.com/c_standard_library/c_function_printf.htm
Unsigned integer type. On 64-bit machines, should be unsigned long long (8 bytes).
https://www.geeksforgeeks.org/size_t-data-type-c-language/ https://stackoverflow.com/questions/2550774/what-is-size-t-in-c
Print size_t
size_t x = ...;
ssize_t y = ...;
printf("%zu\n", x); // prints as unsigned decimal
printf("%zx\n", x); // prints as hex
printf("%zd\n", y); // prints as signed decimal
int foo(int bar)
{
int return_value = 0;
if (!do_something( bar )) {
goto error_1;
}
if (!init_stuff( bar )) {
goto error_2;
}
if (!prepare_stuff( bar )) {
goto error_3;
}
return_value = do_the_thing( bar );
error_3:
cleanup_3();
error_2:
cleanup_2();
error_1:
cleanup_1();
return return_value;
}
https://stackoverflow.com/questions/788903/valid-use-of-goto-for-error-management-in-c
goto label;
...
label:
...
https://www.geeksforgeeks.org/goto-statement-in-c-cpp/
Use sigaction(). signal() seems unreliable.
static void install_sigpipe_handler() {
struct sigaction action;
sigset_t block_mask;
sigemptyset(&block_mask);
action.sa_handler = sigpipe_handler;
action.sa_mask = block_mask;
action.sa_flags = SA_RESTART; /* Restart syscalls if possible */
if (sigaction(SIGPIPE, &action, NULL) < 0) {
sio_fprintf(STDERR_FILENO, "Signal error\n");
_exit(1);
}
}
2 = SIGINT (ctrl-c)
http://www.yolinux.com/TUTORIALS/C++Signals.html
If you pass struct as argument, all its contents will be copied. Not a reference unless argument is struct *.
A struct in a function is a local copy.
Enclosing brackets. So variables declared inside if blocks disappear after you leave the block.
https://stackoverflow.com/questions/8543167/scope-of-variables-in-if-statements
Global variables initialized to 0 automatically.
int a; // is set to 0
void foo() {
int b; // set to whatever happens to be in memory there
}
https://stackoverflow.com/questions/7975008/initializing-variables-in-c
Ignore data read (don't store in variable):
sscanf(line, " %c %lx,%*d", &c, &address);
https://www.tutorialspoint.com/c_standard_library/c_function_sscanf.htm
\60 // octal for '0'
%f - double
%lx - print long in hex
%ld - print long in decimal
%o - octal integer
%p - pointer address
%x - unsigned hex integer
https://stackoverflow.com/questions/38561/what-is-the-argument-for-printf-that-formats-a-long https://www.lix.polytechnique.fr/~liberti/public/computing/prog/c/C/FUNCTIONS/format.html https://stackoverflow.com/questions/4264127/correct-format-specifier-for-double-in-printf http://www.cplusplus.com/reference/cstdio/printf/
typedef int Length;
typedef struct foo_node node;
struct foo_node {
node *next;
node *prev;
};
They are private to the file (and any files that include the file). You cannot have a "static" typedef.
https://stackoverflow.com/questions/12444611/using-static-on-typedef-struct
sizeof unary-expression
sizeof ( type-name )
https://stackoverflow.com/questions/5894892/why-and-when-do-i-need-to-use-parentheses-after-sizeof
#include <stdio.h>
int fileno(FILE *stream)
#include <stdio.h>
int main ( void ) {
static const char filename[] = "file.txt";
FILE *file = fopen ( filename, "r" );
if ( file != NULL ) {
char line [ 128 ]; /* or other suitable maximum line size */
while ( fgets ( line, sizeof line, file ) != NULL ) { /* read a line */
fputs ( line, stdout ); /* write the line */
}
fclose ( file );
} else {
perror ( filename ); /* why didn't the file open? */
}
return 0;
}
https://www.daniweb.com/programming/software-development/code/216411/reading-a-file-line-by-line
int val = atoi(str);
https://www.tutorialspoint.com/c_standard_library/c_function_atoi.htm
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int
main (int argc, char **argv)
{
int aflag = 0;
int bflag = 0;
char *cvalue = NULL;
int index;
int c;
opterr = 0;
while ((c = getopt (argc, argv, "abc:")) != -1)
switch (c)
{
case 'a':
aflag = 1;
break;
case 'b':
bflag = 1;
break;
case 'c':
cvalue = optarg;
break;
case '?':
if (optopt == 'c')
fprintf (stderr, "Option -%c requires an argument.\n", optopt);
else if (isprint (optopt))
fprintf (stderr, "Unknown option `-%c'.\n", optopt);
else
fprintf (stderr,
"Unknown option character `\\x%x'.\n",
optopt);
return 1;
default:
abort ();
}
printf ("aflag = %d, bflag = %d, cvalue = %s\n",
aflag, bflag, cvalue);
for (index = optind; index < argc; index++)
printf ("Non-option argument %s\n", argv[index]);
return 0;
}
https://www.gnu.org/software/libc/manual/html_node/Example-of-Getopt.html
char *strcat(char *dest, const char *src)
Requires dest to have enough space for src to be appended. Seems to need one more than the final string length in order to write the \0 character.
https://www.tutorialspoint.com/c_standard_library/c_function_strcat.htm
fork()
http://www.csl.mtu.edu/cs4411.ck/www/NOTES/process/fork/create.html
pthread_create
http://timmurphy.org/2010/05/04/pthreads-in-c-a-minimal-working-example/ https://stackoverflow.com/questions/56810/how-do-i-start-threads-in-plain-c