init

.gitignore

@@ -0,0 +1 @@
+.vscode

memfun.c

@@ -0,0 +1,16 @@
+#include <stdio.h>
+#include <string.h>
+
+int main() {
+    char c[7];
+
+    strcpy(c, "foobar");
+
+    printf("Hello World Foobar: %s\n", c);
+
+    for (char* i = c; i < c + 7; i++) {
+        printf("Mem address: %d\tContent: %c\n", i, *i);
+    }
+
+    return 0;
+}

pythagoras.c

@@ -0,0 +1,17 @@
+#include <stdio.h>
+#include <math.h>
+
+int main() {
+    int a, b;
+    double c;
+
+    printf("a? ");
+    scanf("%d", &a);
+
+    printf("b? ");
+    scanf("%d", &b);
+
+    c = sqrt((a*a) + (b*b));
+
+    printf("c: %f\n", c);
+}

pythagoras_nice.c

@@ -0,0 +1,20 @@
+#include <stdio.h>
+#include <math.h>
+
+double pythagoras(int *a, int *b) {
+    // c is strange
+    return sqrt(*a**a + *b**b);
+}
+
+int main() {
+    for (int a = 1; a < 10; a++) {
+        for (int b = a; b < 10; b++) {
+            double c = pythagoras(&a, &b);
+            if (c == (int)c) {
+                printf("square root of %d² and %d²: %f\n", a, b, c);
+            }
+        }
+    }
+
+    return 0;
+}

readfile.c

@@ -0,0 +1,61 @@
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+
+const unsigned MAX_BUFFER_LENGTH = 256;
+
+void trim(char *string) {
+    if (string[strlen(string) - 1] == '\n') {
+        string[strlen(string) - 1] = '\0';
+        trim(string);
+    }
+}
+
+int main() {
+    char *filename = "test/text1.txt";
+
+    FILE *fp = fopen(filename, "r");
+
+    if (fp == NULL) {
+        printf("Error opening file %s\n", filename);
+        return EXIT_FAILURE;
+    }
+
+    char buffer[MAX_BUFFER_LENGTH];
+    char *line = NULL;
+    while (fgets(buffer, MAX_BUFFER_LENGTH, fp)) {
+        trim(buffer);
+
+        char *tmpLine;
+        if (line == NULL) {
+            int newLineSize = strlen(buffer);
+            printf("line is null; new size %d\n", newLineSize);
+            tmpLine = calloc(sizeof(char), newLineSize + 1);
+        } else {
+            int newLineSize = strlen(buffer) + strlen(line);
+            printf("line is NOT null; new size %d\n", newLineSize);
+            tmpLine = realloc(line, newLineSize + 1);
+        }
+
+        if (tmpLine != NULL) {
+            line = tmpLine;
+        } else {
+            return 1;
+        }
+        strcat(line, buffer);
+
+        // check for possible overflow
+        if (strlen(buffer) + 1 >= MAX_BUFFER_LENGTH) {
+            // no edge limit problem because trim is cutting buffer if there is a "\n" on the end
+            printf("!!!Overflow detected!!!\n");
+        } else {
+            printf("read line (%ld): %s\n", strlen(line), line);
+            free(line);
+            line = NULL;
+        }
+    }
+
+    fclose(fp);
+
+    return EXIT_SUCCESS;
+}

tcp.c

@@ -0,0 +1,115 @@
+#include <arpa/inet.h>
+#include <sys/socket.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <errno.h>
+#include <string.h>
+#include <netdb.h>
+#include <unistd.h>
+
+#define SERVER "devloop.de"
+#define PORT 25
+
+#define RECEIVE_BUFFER 256
+
+char* copyNtrim(char *str) {
+    char *ret = strdup(str);
+
+    for (int i = strlen(ret); i >= 0; i--) {
+        if (ret[i] == '\r' || ret[i] == '\n') {
+            ret[i] = '\0';
+        }
+    }
+
+    return ret;
+}
+
+void sendMessage(int sock, char *msg) {
+    int sendBytes = send(sock, msg, strlen(msg), 0);
+    if (sendBytes >= 0) {
+        printf("Send %d bytes to %s:%d: %s\n", sendBytes, SERVER, PORT, copyNtrim(msg));
+    } else {
+        fprintf(stderr, "Failed to send message to %s:%d (%d): %s", SERVER, PORT, errno, strerror(errno));
+        exit(EXIT_FAILURE);
+    }
+}
+
+void receiveMessage(int sock, char *buf, int bufLen) {
+    int recvBytes = recv(sock, buf, bufLen, 0);
+    if (recvBytes >= 0) {
+        printf("Received %d bytes from %s: %s\n", recvBytes, SERVER, copyNtrim(buf));
+    } else {
+        fprintf(stderr, "Error receiving data from %s (%d): %s", SERVER, errno, strerror(errno));
+        exit(EXIT_FAILURE);
+    }
+}
+
+struct sockaddr_in6* lookup(char *host) {
+    int err;
+
+    // lookup IPv6 address
+    struct addrinfo hints;
+    struct addrinfo *serverAddrs;
+    memset(&hints, 0, sizeof(hints));
+    hints.ai_family = AF_INET6;
+    hints.ai_socktype = SOCK_STREAM;
+    err = getaddrinfo(host, NULL, &hints, &serverAddrs);
+    if (err) {
+        fprintf(stderr, "Error looking up host %s (%d): %s\n", host, err, gai_strerror(err));
+        exit(EXIT_FAILURE);
+    }
+
+    // print out IPv6 addresses
+    struct addrinfo *serverAddr;
+    struct sockaddr_in6 *serverAddr_in6;
+    for (serverAddr = serverAddrs; serverAddr != NULL; serverAddr = serverAddr->ai_next) {
+        serverAddr_in6 = (struct sockaddr_in6 *)serverAddr->ai_addr;
+        unsigned char buf[sizeof(struct in6_addr)];
+        char serverAddr_str[INET6_ADDRSTRLEN];
+        printf("IPv6 of %s: %s\n", host, inet_ntop(AF_INET6, &serverAddr_in6->sin6_addr, serverAddr_str, INET6_ADDRSTRLEN));
+    }
+
+    return serverAddr_in6;
+}
+
+int connectTo(char *host, int port) {
+    int err;
+
+    // socket
+    int sock = socket(AF_INET6, SOCK_STREAM, 0);
+    if (sock == -1) {
+        fprintf(stderr, "Error creating socket (%d): %s\n", errno, strerror(errno));
+        exit(EXIT_FAILURE);
+    }
+
+    struct sockaddr_in6 *serverAddr_in6 = lookup(host);
+
+    // connect last IPv6 address
+    serverAddr_in6->sin6_port = htons(port);
+    err = connect(sock, (struct sockaddr *)serverAddr_in6, sizeof(*serverAddr_in6));
+    if (err) {
+        fprintf(stderr, "Error connecting %s:%d (%d): %s\n", host, port, err, gai_strerror(err));
+        exit(EXIT_FAILURE);
+    }
+
+    return sock;
+}
+
+int main() {
+    char buf[RECEIVE_BUFFER];
+
+    // connect
+    int sock = connectTo(SERVER, PORT);
+    
+    // chat
+    receiveMessage(sock, buf, RECEIVE_BUFFER);
+    sendMessage(sock, "HELO tuxic.dyndns.devloop.de\r\n");
+    receiveMessage(sock, buf, RECEIVE_BUFFER);
+    sendMessage(sock, "QUIT\r\n");
+    receiveMessage(sock, buf, RECEIVE_BUFFER);
+
+    // end session
+    close(sock);
+
+    exit(EXIT_SUCCESS);
+}

test/text1.txt

@@ -0,0 +1,5 @@
+foo
+bar
+moep blah
+aaaaaaaaaabbbbbbbbbbaaaaaaaaaabbbbbbbbbbaaaaaaaaaabbbbbbbbbbaaaaaaaaaabbbbbbbbbbaaaaaaaaaabbbbbbbbbbaaaaaaaaaabbbbbbbbbbaaaaaaaaaabbbbbbbbbbaaaaaaaaaabbbbbbbbbbaaaaaaaaaabbbbbbbbbbaaaaaaaaaabbbbbbbbbbaaaaaaaaaabbbbbbbbbbaaaaaaaaaabbbbbbbbbbaaaaaaaaaabbbbbbbbbb
+aaaaaaaaaabbbbbbbbbbaaaaaaaaaabbbbbbbbbbaaaaaaaaaabbbbbbbbbbaaaaaaaaaabbbbbbbbbbaaaaaaaaaabbbbbbbbbbaaaaaaaaaabbbbbbbbbbaaaaaaaaaabbbbbbbbbbaaaaaaaaaabbbbbbbbbbaaaaaaaaaabbbbbbbbbbaaaaaaaaaabbbbbbbbbbaaaaaaaaaabbbbbbbbbbaaaaaaaaaabbbbbbbbbbaaaaaaaaaa1234

test/text2.txt

@@ -0,0 +1,9 @@
+Zeile
+1
+111
+1
+1
+foo
+bar
+moep
+.

writefile.c

@@ -0,0 +1,29 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+
+#define _FILE "test/text2.txt"
+
+int main() {
+    FILE *fp = fopen(_FILE, "w");
+
+    if (fp == NULL) {
+        char *buf = malloc(256);
+        sprintf(buf, "Error opening file `%s`", _FILE);
+        perror(buf);
+        return EXIT_FAILURE;
+    }
+
+    char input[256];
+    printf("Enter text...\n");
+    do {
+        scanf("%s", input);
+        printf("Length of input: %ld\n", strlen(input));
+        fprintf(fp, "%s\n", input);
+        fflush(fp);
+    } while (strlen(input) > 0 && input[0] != '.');
+
+    fclose(fp);
+
+    return EXIT_SUCCESS;
+}