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Kenneth: Created page with "== C Programming Language == C Programming Language (2nd Edition) (Prentice Hall Software) (Paperback)] * Note: The definitive C guide. Has printf("Hello World\n"); 2015-10-27T20:34:05Z Created page with "== C Programming Language == C Programming Language (2nd Edition) (Prentice Hall Software) (Paperback)] * Note: The definitive C guide. Has <code>printf("Hello World\n");</c..." New page == C Programming Language == C Programming Language (2nd Edition) (Prentice Hall Software) (Paperback)] * Note: The definitive C guide. Has <code>printf("Hello World\n");</code> original example == C# == Are you looking for [[C Sharp]]? == Hello World == [http://en.wikipedia.org/wiki/Hello_world Hello world program - Wikipedia] main() { printf("hello, world\n"); } [http://en.wikipedia.org/wiki/The_C_Programming_Language_(book) The C Programming Language (book) - Wikipedia] :"Perhaps the most famous example program from the book is its "hello world" program, which just prints out the text "hello, world" to the terminal, as an illustration of a minimal working C program. Numerous texts since then have followed that convention for introducing a programming language." == gcc == See [[gcc]] == Code == === Hello World === <pre> #include <stdio.h> int main() { printf("Hello World\n"); return 0; } </pre> === Variables === int i = 1; float f = 1.0; char c = 'a'; char s[] = "Hello"; char p = "Hi"; === Print === #include <stdio.h> printf("int:%d float:%.2f char:%c string:%s string:%s", i, f, c, s, p); === Parameters === <pre> int main(int argc, char argv[]) { int i; printf("CMD Args: %d\n", argc); for(i = 0 ; i < argc ; i++) printf("CMD Arg %d = %s\n", i, argv[i]); // 0 = ./test } </pre> === Array === Basic int array, initialization and length <pre> #include <stdio.h> int main() { // won't work for dymanic allocated memory #define ARRAY_LENGTH(x) (sizeof(x) / sizeof(x[0])) int int_array[10];// = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}; // int int_array[10] = { 0 }; // all elements 0 // int array_length = sizeof(int_array) / sizeof(int_array[0]); int array_length = ARRAY_LENGTH(int_array); int i; for (i = 0 ; i < array_length ; i++) int_array[i] = i; // 40, 4, 10 printf("total length:%d, int size:%d, array length:%d\n", sizeof(int_array), sizeof(int_array[0]), array_length); for (i = 0 ; i < array_length ; i++) printf("%d = %d\n", i, int_array[i]); } </pre> Note: Arrays are passed as points to functions (Pass by Reference), so modifying an array within a function will modify the original. Basic char array, initialization and length <pre> #include <stdio.h> #define ARRAY_LENGTH(x) (sizeof(x) / sizeof(x[0])) int ord(char c) { return (unsigned char)c; } char chr(int n) { return (unsigned char)n; } int main() { int i; // SEVERAL WAYS TO INITIALIZE: //char char_array[4] = {'O', 'O', 'O', '\0'}; //char char_array[4] = "OOO"; // don't forget ending \0 //char char_array[] = "OOO"; // size is 4 for \0 //char char_array[3]; //for (i = 0 ; i < ARRAY_LENGTH(char_array) ; i++) // char_array[i] = 'O'; //char char_array[10] = { 0 }; // all elements 0 //char char_array[10] = {'O', 'O'}; // auto fills rest with \0, how nice, but can this be trusted? char char_array[10] = {[0 ... 9] = 'X'}; // All 'X' // int array_length = sizeof(char_array) / sizeof(char_array[0]); int array_length = ARRAY_LENGTH(char_array); // 40, 1, 4 printf("total length:%d, char size:%d, array length:%d\n", sizeof(char_array), sizeof(char_array[0]), array_length); for (i = 0 ; i < array_length ; i++) printf("%d = %c [%d][%d]\n", i, char_array[i], char_array[i], ord(char_array[i])); } </pre> References: * How do I determine the size of my array in C? - Stack Overflow - http://stackoverflow.com/questions/37538/how-do-i-determine-the-size-of-my-array-in-c * Convert char to int in C and C++ - Stack Overflow - http://stackoverflow.com/questions/5029840/convert-char-to-int-in-c-and-c * How to initialize an array in C - Stack Overflow - http://stackoverflow.com/questions/201101/how-to-initialize-an-array-in-c === Random === FAQ > Generate random numbers? - Cprogramming.com [http://faq.cprogramming.com/cgi-bin/smartfaq.cgi?answer=1042005782&id=1043284385] <pre> #include <stdio.h> #include <stdlib.h> #include <time.h> int main(void) { int i; srand(time(NULL)); i = rand(); printf ("Your random number is %d\n", i); printf ("This compiler can generate random numbers from 0 to %d\n", RAND_MAX); return(0); } </pre> Get number between two numbers: <pre> /* * Formula: * rand() % N <- To get a number between 0 - N-1 * Then add the result to min, giving you * a random number between min - max. / rc = (rand() % (max - min + 1) + min); </pre> === Pointers === Simple int pointer: <pre> void mod_ptr(int mptr) { printf("%d\n", mptr); // 3 mptr = 4; printf("%d\n", mptr); // 4 int t = 5; mptr = t; printf("%d\n", mptr); // 5 } int main() { int ptr; ptr = 1; printf("%d\n", ptr); // 1 int tmp_num = 2; ptr = tmp_num; // get value printf("%d\n", ptr); // 2 int tmp_num = 2; ptr = &tmp_num; // get address printf("%d\n", ptr); // 2 ptr = 3; mod_ptr(ptr); printf("%d\n", ptr); // 5 int n; n = ptr; printf("%d\n", n); // 5 } </pre> References: * A Beginner's Guide to Pointers - CodeProject - http://www.codeproject.com/Articles/627/A-Beginner-s-Guide-to-Pointers * Pointers - C++ Documentation - http://www.cplusplus.com/doc/tutorial/pointers/ === Function Pointers === References: * The Function Pointer Tutorials - Index - http://www.newty.de/fpt/index.html * Function pointer - Wikipedia, the free encyclopedia - https://en.wikipedia.org/wiki/Function_pointer == C for C++ Programmers == Source: [http://people.cs.uchicago.edu/~iancooke/osstuff/ccc.html C for C++ Programmers] === Hello World === #include <stdio.h> int main() { printf("Hello World"); } === Output === printf("the variable 'i' is: %d", i); sequence type : produces %d or %i - int : signed decimal notation %s - char * : prints characters until the null character is reached %x - int : hexidecimal notation %p - void * : prints as a pointer C++ C cin stdin cout stdout cerr stderr int fputs(const char str, FILE stream); if ( (fputs("Hello world", stdout)) == EOF) { fprint(stderr, "Whoops, something went wrong"); } === Input === Input is a bit trickier. For reading an entire line you'll probably want to use fgets(). Here's the prototype: char fgets(char buffer, int size, FILE stream); fgets() reads up to size-1 characters from stream and stores them in buffer. fgets() stores the null character ('\0') after the last character read into the buffer and returns 'buffer' if everything works fine, or NULL on error or end of file. Here's an example: char cptr; char buffer[256]; printf("Enter some stuff:\n"); cptr = fgets(buffer, 256, stdin); if(cptr != NULL) { printf("You typed : %s\n", cptr); } === Command Line Arguments === <pre> #include <stdio.h> int main(int argc, char argv[]) { // argc - count of parameters, include program name // argv - array of arguments, argv[0] is program name if(argc == 2) { printf("Hello %s\n", argv[0]); } else { printf("Usage: %s [name]\n", argv[0]); } } </pre> === Memory Allocation === void malloc(int nbytes) /* We're going to allocate enough space for an integer and assign 5 to that memory location / int foo; /* malloc call: note the cast of the return value from a void * to the appropriate pointer type / foo = (int ) malloc(sizeof(int)); foo = 5; / Here we're allocating space for 5 integers / int foo; foo = (int ) malloc(sizeof(int) 5); foo[0] = 17; foo[4] = 22; void free(void ); free(foo); <pre> #define SIZE_N 10241024 // 1M #define SIZE_M 25637 ... char ptr; if( ( ptr = calloc( SIZE_N, SIZE_M ) ) == NULL ) { printf("Error allocating memory!\n"); exit(1); } ... free(ptr); </pre> === Constants === #define MAX_LEN 1024 #define NUM_CALLS 20 === structs === struct point { int x; int y; }; acceptable usage: struct point p; p.x = 0; p.y = 0; preferred usage: struct point p; p = (struct point ) malloc(sizeof(struct point)); p->x = 0; p->y = 0; remove struct repetition with typedef: typdef struct point Point; Point p; p = (Point ) malloc(sizeof(Point); p->x = 0; === Libraries === #include <stdlib.h> #include <string.h> == Notes == === printf formatting === <pre> %[flags][min field width][precision][length]conversion specifier ----- --------------- --------- ------ ------------------- \ #,* .#, .* / \ \ / \ #,0,-,+, ,',I hh,h,l,ll,j,z,L c,d,u,x,X,e,f,g,s,p,%</b> ------------- --------------- ----------------------- # | Alternate, hh | char, c | unsigned char, 0 | zero pad, h | short, d | signed int, - | left align, l | long, u | unsigned int, + | explicit + - sign, ll | long long, x | unsigned hex int, | space for + sign, j | [u]intmax_t, X | unsigned HEX int, ' | locale thousands grouping, z | size_t, e | [-]d.ddde±dd double, I | Use locale's alt digits t | ptrdiff_t, E | [-]d.dddE±dd double, L | long double, ---------===== if no precision => 6 decimal places / f | [-]d.ddd double, if precision = 0 => 0 decimal places _____/ g | e|f as appropriate, if precision = # => # decimal places G | E|F as appropriate, if flag = # => always show decimal point s | string, ..............------ / p | pointer, if precision => max field width / % | % </pre> Source: [http://www.pixelbeat.org/programming/gcc/format_specs.html printf format specifications quick reference] More at: [http://www.cplusplus.com/reference/clibrary/cstdio/printf/ printf - C++ Reference] === malloc vs calloc === Conceptually, calloc works like this: [http://www.daniweb.com/forums/thread180535.html#] void calloc ( size_t n, size_t size ) { void mem = malloc ( n * size ); memset ( mem, 0, n * size ); return mem; } === Array of pointers === Array of pointers: [http://www.roseindia.net/c-tutorials/array-string-using-pointer.shtml] <pre> #include <stdio.h> #include <conio.h> void main() { clrscr(); char array[2]; array[0]="Hello"; array[1]="World"; printf("The Array of String is = %s,%s\n", array[0], array[1]); getch(); } </pre> == My Code == === fork === <pre> if(fork()) printf("I am the parent!"); / A non-zero indicates the parent process / else printf("I am the child!"); / A zero indicates the child process / </pre> === parameters === === signals === === Bloat Memory === <pre> #include <stdlib.h> #include <stdio.h> #define BLOAT_ARRAY_SIZE 100000 // 10K #define BLOAT_SIZE 10241024 // 1MB typedef struct { char bloat[BLOAT_SIZE]; } bloat_struct; int main() { bloat_struct bloat_array[BLOAT_ARRAY_SIZE]; // array of bloated structures printf("Bloat Array Size: %d\n", BLOAT_ARRAY_SIZE); printf("Bloat Size: %d\n", BLOAT_SIZE); int i, j; // loop variables for( i=0 ; i<BLOAT_ARRAY_SIZE ; i++ ) { // allocate memory for bloated structure //if( ( bloat_array[i] = (bloat_struct ) malloc( sizeof(bloat_struct) ) ) == NULL ) if( ( bloat_array[i] = (bloat_struct ) calloc( sizeof(bloat_struct), 1 ) ) == NULL ) printf("Error allocating bloat: #%d\n", i); // use allocated memory //for( j = 0 ; j<BLOAT_ARRAY_SIZE ; j++ ) // bloat_array[i]->bloat[j] = '1'; } printf("Memory has been consumed to %d %d = %.0f bytes.\n", BLOAT_SIZE, BLOAT_ARRAY_SIZE, (double) BLOAT_SIZE * BLOAT_ARRAY_SIZE); printf("Press enter to free the memory . . . "); char input; char buff[256]; input = fgets(buff, sizeof(buff), stdin); // free allocated memory for( i=0 ; i<BLOAT_ARRAY_SIZE ; i++ ) { free(bloat_array[i]); } return 0; } </pre> <pre> Memory consumed: 1073741824 Press enter to free the memory . . . [root@adaptecweb ~]# gcc eatmem2.c -o eatmem2 ; if [ $? = 0 ] ; then ./eatmem2 ; fi #include <stdio.h> #include <stdlib.h> #define BLOAT_ARRAY_SIZE 1024 // 1K #define BLOAT_SIZE 10241024 // 1MB int main() { char bloat_array[BLOAT_ARRAY_SIZE]; // array of pointers char buff[1024]; // buffer for readline printf("Object count: %d\n", BLOAT_ARRAY_SIZE); printf("Object size:: %d\n", BLOAT_SIZE); printf("Memory consumed: %.0f\n", (double) BLOAT_SIZE BLOAT_ARRAY_SIZE); printf("\n"); int i, j; // loop variables if( ( bloat_array[0] = calloc( BLOAT_SIZE, BLOAT_ARRAY_SIZE ) ) == NULL ) printf("Error!"); /* for( i=0 ; i<BLOAT_ARRAY_SIZE ; i++ ) { // allocate and zero fill memory for each object if( ( bloat_array[i] = calloc( BLOAT_SIZE, 1 ) ) == NULL ) printf("Error allocating memory! (#%d)\n", i); } / printf("Press enter to free the memory . . . "); fgets(buff, sizeof(buff), stdin); free(bloat_array[0]); return 0; // free allocated memory for( i=0 ; i<BLOAT_ARRAY_SIZE ; i++ ) { free(bloat_array[i]); } //printf("Press enter to free the exit . . . "); //fgets(buff, sizeof(buff), stdin); return 0; } </pre> <pre> #include <stdio.h> #include <stdlib.h> #define BLOAT_ARRAY_SIZE 1024 // 1K #define BLOAT_SIZE 10241024 // 1MB int main() { char bloat_array[BLOAT_ARRAY_SIZE]; // array of pointers char buff[1024]; // buffer for readline printf("Object count: %d\n", BLOAT_ARRAY_SIZE); printf("Object size:: %d\n", BLOAT_SIZE); printf("Memory consumed: %.0f\n", (double) BLOAT_SIZE BLOAT_ARRAY_SIZE); printf("\n"); int i, j; // loop variables for( i=0 ; i<BLOAT_ARRAY_SIZE ; i++ ) { // allocate and zero fill memory for each object if( ( bloat_array[i] = calloc( BLOAT_SIZE, 1 ) ) == NULL ) printf("Error allocating memory! (#%d)\n", i); } printf("Press enter to free the memory . . . "); fgets(buff, sizeof(buff), stdin); // free allocated memory for( i=0 ; i<BLOAT_ARRAY_SIZE ; i++ ) { free(bloat_array[i]); } //printf("Press enter to free the exit . . . "); //fgets(buff, sizeof(buff), stdin); return 0; } </pre> <pre> #include <stdio.h> #include <stdlib.h> #define SIZE_N 10241024 // 1M #define SIZE_M 12612 int main() { char ptr; printf("Allocating %.0f bytes.\n", (double) SIZE_N SIZE_M); if( ( ptr = calloc( SIZE_N, SIZE_M ) ) == NULL ) { printf("Error allocating memory!\n"); exit(1); } printf("Press enter to free the memory . . . "); char buff[1024]; // buffer for readline fgets(buff, sizeof(buff), stdin); // free allocated memory free(ptr); return 0; } </pre> == keywords == [[Category:Programming]]