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140 lines
3.8 KiB
140 lines
3.8 KiB
#include <stdlib.h>
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#include <stdio.h>
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#include <string.h>
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// summary ofstring placement
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/*
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char *globalHeader = "Chapter";
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char globalArrayHeader[] = "Chapter";
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void displayHeader() {
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static char *staticHeader = "Chapter";
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char *localHeader = "Chapter";
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static char staticArrayHeader[] = "Chapter";
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char localArrayHeader[] = "Chapter";
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char *heapHeader = malloc(strlen("Chapter")+1);
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strcpy(heapHeader, "Chapter");
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}
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*/
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int main(void) {
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// print size of char & character literal
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printf("%zu\n", sizeof(char));
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printf("%zu\n", sizeof('a'));
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// when a string is not a constant
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// doesn't work with gcc anymore, also with -Wno-deprecated-writable-strings
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// gives 'Bus error: 10'
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{
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char *tabHeader = "Sound";
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//*tabHeader = 'L';
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printf("%s\n", tabHeader);
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}
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// string initialization
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{
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// array of char
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char header[] = "Media Player";
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printf("%s\n", header);
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header[0] = 'W';
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header[1] = 'u';
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header[2] = 'r';
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header[3] = 's';
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header[4] = 't';
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header[5] = '\0';
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printf("%s\n", header);
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// pointer to char (with memory allocation)
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char *headerPtr = malloc(strlen("Media Player") + 1);
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if (headerPtr != NULL) {
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strcpy(headerPtr, "Media Player");
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printf("%s\n", headerPtr);
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*headerPtr = 'W';
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*(headerPtr + 1) = 'u';
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*(headerPtr + 2) = 'r';
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*(headerPtr + 3) = 's';
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*(headerPtr + 4) = 't';
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*(headerPtr + 5) = '\0';
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printf("%s\n", headerPtr);
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for (size_t j = 0; j < strlen(headerPtr); j++) {
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printf("headerPtr[%zu] Address: %p Value: %c\n", j, &headerPtr[j], headerPtr[j]);
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}
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printf("\n");
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free(headerPtr);
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}
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// direct init with character pointer
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// don't create a new copy, instead a reference to string literal pool only
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char *headerRef = "Media Player";
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printf("%s\n", headerRef);
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// you shouldn't assign a char pointer with a character literal
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// because character literals is of type int
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// wrong:
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// char *prefix = '+';
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// better:
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char *prefix = malloc(2);
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if (prefix != NULL) {
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*prefix = '+';
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*(prefix + 1) = 0;
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printf("%s\n", prefix);
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free(prefix);
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}
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// string initialisation from standard in
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// don't forget to allocate memory before read from standard in
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// wrong:
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// char *command;
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// printf("%s: ", "Enter a command");
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// scanf("%s", command);
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// better:
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char *command = malloc(11);
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if (command != NULL) {
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printf("%s: ", "Enter a command (max. 10 chars): ");
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scanf("%10s", command);
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printf("You entered: %s with length: %zu\n", command, strlen(command));
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free(command);
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}
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// memset buffer overflow test
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// executes without warnings or errors on osx :D
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char *mem = malloc(11);
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if (mem != NULL) {
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memset(mem, 0x42, 16);
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for (size_t i = 0; i < 16; i++) {
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printf("mem[%zu] Address: %p : %c\n", i, &mem[i], mem[i]);
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}
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free(mem);
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}
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}
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#define KERNEL_PANIC 0x0000
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char *mem = (int*) KERNEL_PANIC;
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// standard string operations
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// comparing strings
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{
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char command[16];
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printf("Enter a command: ");
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scanf("%15s", command);
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// return value of strlen == 0 -> strings are equal
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if (!strcmp(command, "quit")) {
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printf("The command was quit\n");
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} else {
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printf("The command wasn't quit\n");
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}
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}
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return 0;
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}
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