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--- os_cp:open:solutions [2023/03/28 22:06]
jkonczak utworzono
+++ — (aktualna)
@@ Linia 1: / Linia 1: @@
-~~Exercise.#~~
-<code c>
-int main(int argc, char *argv[]){
-    return 0;
-}
-</code>
-To compile, one may use any of:
-  * ''cc prog.c -o prog''
-  * ''gcc   --std=c17 -Wall --pedantic -g -O2 x.c -o x''
-  * ''clang --std=c17 -Wall --pedantic -g -O2 x.c -o x''
-~~Exercise.#~~
-<code c>
-#include <stdio.h>
-int main(int argc, char *argv[]){
-    printf("Hello.\n");
-    return 0;
-}
-</code>
-<code c>
-#include <stdio.h>
-int main(int argc, char *argv[]){
-    fprintf(stdout, "Hello.\n");
-    return 0;
-}
-</code>
-<code c>
-#include <unistd.h>
-int main(int argc, char *argv[]){
-    write(STDOUT_FILENO, "Hello.\n", 7);
-    return 0;
-}
-</code>
-~~Exercise.#~~
-<code c>
-#include <unistd.h>
-#include <string.h>
-int main(int argc, char *argv[]){
-    write(STDOUT_FILENO, argv[1], strlen(argv[1]));
-    write(STDOUT_FILENO, "\n", 1);
-    return 0;
-}
-</code>
-~~Exercise.#~~
-<code c>
-#include <unistd.h>
-#include <string.h>
-int main(int argc, char *argv[]){
-    write(STDOUT_FILENO, argv[1]+3, strlen(argv[1])-3);
-    write(STDOUT_FILENO, "\n", 1);
-    return 0;
-}
-</code>
-~~Exercise.#~~
-<code c>
-#include <unistd.h>
-#include <string.h>
-int main(int argc, char *argv[]){
-    for(int i = 0; i < argc; ++i){
-        write(STDOUT_FILENO, argv[i], strlen(argv[i]));
-        write(STDOUT_FILENO, "\n", 1);
-    }
-    return 0;
-}
-</code>
-or, knowing that the argument array has a [[https://en.wikipedia.org/wiki/Sentinel_value|sentinel]]:
-<code c>
-#include <unistd.h>
-#include <string.h>
-int main(int argc, char *argv[]){
-    do {
-        write(STDOUT_FILENO, *argv, strlen(*argv));
-        write(STDOUT_FILENO, "\n", 1);
-    } while(*++argv);
-    return 0;
-}
-</code>
-~~Exercise.#~~
-<code c>
-#include <unistd.h>
-#include <string.h>
-int main(int argc, char *argv[]){
-    char buffer[256];
-    strncpy(buffer, argv[1], 254);
-    buffer[254] = 0;
-    strcat(buffer, "\n");
-    write(STDOUT_FILENO, buffer, strlen(buffer));
-    return 0;
-}
-</code>
-~~Exercise.#~~
-<code c>
-#include <unistd.h>
-#include <stdlib.h>
-#include <string.h>
-int main(int argc, char *argv[]){
-    size_t length = strlen(argv[1]);
-    char *buffer = (char*) malloc(length+1);
-    memcpy(buffer, argv[1], length);
-    buffer[length]='\n';
-    write(STDOUT_FILENO, buffer, strlen(buffer));
-    free(buffer);
-    return 0;
-}
-</code>
-~~Exercise.#~~
-<code c>
-#include <unistd.h>
-#include <ctype.h>
-#include <stdlib.h>
-#include <string.h>
-int main(int argc, char *argv[]){
-    size_t length = strlen(argv[1]);
-    char *buffer = (char*) malloc(length+1);
-    for(int i = 0; i < length; ++i)
-        buffer[i] = toupper(argv[1][i]);
-    buffer[length]='\n';
-    write(STDOUT_FILENO, buffer, length+1);
-    free(buffer);
-    return 0;
-}
-</code>
-~~Exercise.#~~
-<code c>
-#include <unistd.h>
-#include <stdio.h>
-#include <string.h>
-int main(int argc, char *argv[]){
-    char buffer[256];
-    scanf("%254[^\n]", buffer);
-    strcat(buffer, "\n");
-    write(STDOUT_FILENO, buffer, strlen(buffer));
-    return 0;
-}
-</code>
-<code c>
-#include <unistd.h>
-#include <stdio.h>
-#include <string.h>
-int main(int argc, char *argv[]){
-    char buffer[256];
-    fscanf(stdin, "%254[^\n]", buffer);
-    strcat(buffer, "\n");
-    write(STDOUT_FILENO, buffer, strlen(buffer));
-    return 0;
-}
-</code>
-<code c>
-#include <unistd.h>
-int main(int argc, char *argv[]){
-    char buffer[256];
-    int length = read(STDIN_FILENO, buffer, 256);
-    write(STDOUT_FILENO, buffer, length);
-    return 0;
-}
-</code>
-~~Exercise.#~~
-<code c>
-#include <unistd.h>
-#include <stdio.h>
-int main(int argc, char *argv[]){
-    char buffer[256];
-    while(1){
-        int length = read(STDIN_FILENO, buffer, 256);
-        if(length == -1){
-            perror(NULL);
-            return 1;
-        }
-        if(length == 0)
-            break;
-        write(STDOUT_FILENO, buffer, length);
-    }
-    return 0;
-}
-</code>
-~~Exercise.#~~
-<code c>
-#include <unistd.h>
-#include <stdio.h>
-int readFile(){
-    char buffer[256];
-    while(1){
-        int length = read(STDIN_FILENO, buffer, 256);
-        if(length == -1){
-            perror(NULL);
-            return 1;
-        }
-        if(length == 0)
-            return 0;
-        write(STDOUT_FILENO, buffer, length);
-    }
-}
-int main(int argc, char *argv[]){
-    if(readFile())
-        return -1;
-    lseek(STDIN_FILENO, 0, SEEK_SET);
-    if(readFile())
-        return -1;
-    return 0;
-}
-</code>
-~~Exercise.#~~
-<code c>
-#include <unistd.h>
-#include <stdio.h>
-int main(int argc, char *argv[]){
-    char buffer[256];
-    while(1){
-        int length = read(4, buffer, 256);
-        if(length == -1){
-            perror(NULL);
-            return 1;
-        }
-        if(length == 0)
-            break;
-        write(STDOUT_FILENO, buffer, length);
-    }
-    return 0;
-}
-</code>
-~~Exercise.#~~
-<code c>
-#include <unistd.h>
-#include <fcntl.h>
-#include <stdio.h>
-int main(int argc, char *argv[]){
-    int fd = open("/tmp/z", O_RDONLY);
-    if(fd == -1){
-        perror(NULL);
-        return 1;
-    }
-    char buffer[256];
-    while(1){
-        int length = read(fd, buffer, 256);
-        if(length == -1){
-            perror(NULL);
-            return 1;
-        }
-        if(length == 0)
-            break;
-        write(STDOUT_FILENO, buffer, length);
-    }
-    close(fd);
-    return 0;
-}
-</code>
-~~Exercise.#~~
-<code c>
-#include <unistd.h>
-#include <fcntl.h>
-#include <stdio.h>
-int main(int argc, char *argv[]){
-    int fd = open(argv[1], O_RDONLY);
-    if(fd == -1){
-        perror(NULL);
-        return 1;
-    }
-    char buffer[256];
-    while(1){
-        int length = read(fd, buffer, 256);
-        if(length == -1){
-            perror(NULL);
-            return 1;
-        }
-        if(length == 0)
-            break;
-        write(STDOUT_FILENO, buffer, length);
-    }
-    close(fd);
-    return 0;
-}
-</code>
-~~Exercise.#~~
-<code c>
-#include <unistd.h>
-#include <fcntl.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-int main(int argc, char *argv[]){
-    int fd = open(argv[1], O_RDONLY);
-    if(fd == -1){
-        perror(NULL);
-        return 1;
-    }
-    int num = 1;
-    int printNumber = 1;
-    while(1){
-        char c;
-        int count = read(fd, &c, 1);
-        if(count == -1){
-            perror(NULL);
-            return 1;
-        }
-        if(count == 0)
-            break;
-        if(printNumber){
-            char numBuf[16];
-            sprintf(numBuf, "%5d ", num++);
-            write(STDOUT_FILENO, numBuf, strlen(numBuf));
-            printNumber=0;
-        }
-        write(STDOUT_FILENO, &c, 1);
-        if(c == '\n')
-            printNumber=1;
-    }
-    close(fd);
-    return 0;
-}</code>
-++++ The program above is intentionally made simple rather than efficient; the program below is more efficient, but has a few more lines. |
-<code c>
-#include <unistd.h>
-#include <fcntl.h>
-#include <stdio.h>
-#include <string.h>
-void checkPrintNl(int *shallPrint, unsigned *number){
-    if(!*shallPrint)
-        return;
-    char buf[12];
-    sprintf(buf, "%5u ", (*number)++);
-    write(STDOUT_FILENO, buf, strlen(buf));
-    *shallPrint=0;
-}
-int main(int argc, char *argv[]){
-    int fd = open(argv[1], O_RDONLY);
-    if(fd == -1){
-        perror(NULL);
-        return 1;
-    }
-    int printLineNum = 1;
-    unsigned lineNum = 1;
-    while(1){
-        char buf[256];
-        int length = read(fd, buf, 256);
-        if(length == -1){
-            perror(NULL);
-            return 1;
-        }
-        if(length == 0)
-            break;
-        char *it = buf, *nlPos;
-        while( (nlPos = memchr(it, '\n', length)) ){
-            checkPrintNl(&printLineNum, &lineNum);
-            int partLen = nlPos+1-it;
-            write(STDOUT_FILENO, it, partLen);
-            length -= partLen;
-            it = nlPos+1;
-            printLineNum = 1;
-        }
-        if(length){
-            checkPrintNl(&printLineNum, &lineNum);
-            write(STDOUT_FILENO, it, length);
-        }
-    }
-    return 0;
-}
-</code>
-++++
-~~Exercise.#~~
-<code c>
-#include <unistd.h>
-#include <fcntl.h>
-#include <stdio.h>
-#include <stdlib.h>
-int main(int argc, char *argv[]){
-    ++argv; --argc; // get rid of program name; simplifies array indexes
-    int *file = malloc(sizeof(int) * argc);
-    int running = 0;
-    for(int i = 0; i < argc; ++i){
-        file[i] = open(argv[i], O_RDONLY);
-        if(file[i] == -1)
-            perror(argv[i]);
-        else
-            running = 1;
-    }
-    while(running){
-        running = 0;
-        for(int i = 0; i < argc; ++i){
-            while(file[i] != -1){
-                char c;
-                int l = read(file[i], &c, 1);
-                if(l <= 0){
-                    if(l == -1)
-                        perror(argv[i]);
-                    close(file[i]);
-                    file[i] = -1;
-                    break;
-                }
-                if(c == '\n'){
-                    running = 1;
-                    break;
-                }
-                write(STDOUT_FILENO, &c, 1);
-            }
-            write(STDOUT_FILENO, (i == argc-1) ? "\n" : "\t", 1);
-        }
-    }
-    free(file);
-    return 0;
-}
-</code>
-++++ The program above is intentionally made simple rather than efficient; the program below is more efficient, but has more lines. |
-NB: speedup of this program vs the one above is way beyond 100x
-<code c>
-#include <unistd.h>
-#include <fcntl.h>
-#include <stdio.h>
-#include <string.h>
-#include <stdlib.h>
-#include <assert.h>
-/** A few words of explanation: each 'read' and 'write' call involves
- * the operating system. Calling the OS is expensive. Thus, I/O is
- * usually buffered. This program buffers both input and output, but
- * to buffer output and still use OS API, one has to buffer I/O oneself.
- */
-#define BUFSIZE 4096
-// ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ OUTPUT BUFFERING ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
-struct { //< custom standard output buffer
-    char b[2*BUFSIZE];
-    size_t c;
-} outBuf;
-void flushOutput(){ //< writes out the standard output buffer
-    if(outBuf.c != write(STDOUT_FILENO, outBuf.b, outBuf.c)){
-        perror("writing to output failed");
-        exit(1);
-    }
-    outBuf.c = 0;
-}
-/** adds data to output buffer and outputs if buffer is sufficiently filled
-  * @warning: this relies on an assumption that count never exceeds BUFSIZE */
-void bufferOutput(char *data, size_t count){
-    assert(count <= BUFSIZE);
-    memcpy(outBuf.b + outBuf.c, data, count);
-    if((outBuf.c += count) >= BUFSIZE)
-        flushOutput();
-}
-// ~ ~ ~ ~ ~ READING LINES FROM INPUT & BUFFERING INPUT ~ ~ ~ ~ ~
-struct myFile {  //< stores state & buffer of a file
-    char *name;  //< used for diagnostics when read returns -1
-    int fd;      //< once the file ends (or read fails), -1 is put here
-    char buf[BUFSIZE];
-    int pos;     //< position where data in buf starts
-    int count;   //< number of bytes in but from pos to end of data
-};
-/// reads from file to buffer, @returns 0 if any data was read, else returns 1
-int readChunk(struct myFile *f){
-    f->pos = 0;
-    f->count = read(f->fd, f->buf, BUFSIZE);
-    if(f->count<=0){
-        if(f->count == -1)
-            perror(f->name);
-        close(f->fd);
-        f->fd = -1;
-        return 1;
-    }
-    return 0;
-}
-/** reads and outputs a line from file,
- * @returns 0 if there is any outstanding data in file, else returns 1 */
-int readAndOutputLine(struct myFile *f){
-    while(1){
-        if(f->fd == -1)
-            return 1;
-        if(f->count == 0)
-            if(readChunk(f))
-                return 1;
-        char *nlPos, *startPos = f->buf+f->pos;
-        if( (nlPos = memchr(startPos, '\n', f->count)) ){
-            int partLen = nlPos-startPos;
-            bufferOutput(startPos, partLen);
-            f->pos   += partLen+1;
-            f->count -= partLen+1;
-            if(f->count)
-                return 0;
-            return readChunk(f);
-        }
-        bufferOutput(startPos, f->count);
-        f->count = 0;
-    }
-}
-// ~ ~ ~ ~ ~ OPENING FILES, LOOPING THROUGH LINES ~ ~ ~ ~ ~
-int main(int argc, char *argv[]){
-    ++argv; --argc; // get rid of program name; simplifies array indexes
-    struct myFile *myFiles = malloc(sizeof(myFiles) * argc);
-    int allFilesEof = 1;
-    for(int i = 0 ; i < argc; ++i){
-        myFiles[i].fd = open(argv[i], O_RDONLY);
-        if(myFiles[i].fd == -1)
-            perror(argv[i]);
-        else {
-            myFiles[i].name = argv[i];
-            allFilesEof &= readChunk(myFiles+i);
-        }
-    }
-    while(!allFilesEof){
-        allFilesEof = readAndOutputLine(myFiles);
-        for(int i = 1 ; i < argc; ++i){
-            bufferOutput("\t", 1);
-            allFilesEof &= readAndOutputLine(myFiles+i);
-        }
-        bufferOutput("\n", 1);
-    }
-    free(myFiles);
-    flushOutput();
-    return 0;
-}
-</code>
-++++
-~~META:
-language = en
-~~

Jan Kończak

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