ncurses的printw（）不起作用

Question

i filled a matrix with strings from a file, that printf() see correctly, but printw() doesn't seem to agree with the rest of the code. it works with normal strings, but with strings from that matrix, it doesn't work.

#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>
#include <ncurses.h>

int main (int argc, char const *argv[])
{
    char** matrice = malloc(sizeof(char*)*51);
    size_t nbytes;
    int i = 0, j = 0;

    FILE* lab = fopen(argv[1], "r");

    while((getline(&matrice[i], &nbytes, lab) != -1))
    {
        i++;
    }
    printf("%s", matrice[0]);
    getchar();
    initscr();          /* Start curses mode        */
    cbreak();           /* Line buffering disabled  */
    keypad(stdscr, TRUE);       /* We get F1, F2 etc..      */
    noecho();           /* Don't echo() while we do getch */
    printw(matrice[0]);
    printw("dummy line"\n);
    refresh();
    getch();
    endwin();
    return EXIT_SUCCESS;
}

Answer 1

This is nothing to do with printw() , you're just not allocating memory correctly. Here:

char** matrice = malloc(sizeof(char*)*51);

you don't allocate any memory for your actual strings. You allocate memory for 51 pointers, but you don't allocate any memory for them to point to. Your getline() call is therefore trying to read into unallocated memory, which yields undefined behavior. All bets are off until you get your program behaving properly.

You'll need to allocate some memory for each of those 51 pointers, or just use a static array.

As written, you also fail to free() the memory you malloc() at the end, and you fail to check the return value from malloc() to check if it actually gave you the memory.

Something like this is what you want:

#include <stdio.h>
#include <stdlib.h>

#define ARRSIZE 51
#define STRSIZE 100

int main(void) {
    int i;

    char ** matrice = malloc(ARRSIZE * sizeof(*matrice));
    if ( matrice == NULL ) {
        fputs("Couldn't allocate memory!", stderr);
        return EXIT_FAILURE;
    }

    for ( i = 0; i < ARRSIZE; ++i ) {
        matrice[i] = malloc(STRSIZE);
        if ( matrice[i] == NULL ) {
            fputs("Couldn't allocate memory!", stderr);
            return EXIT_FAILURE;
        }
    }

    /* Rest of your program */

    for ( i = 0; i < ARRSIZE; ++i ) {
        free(matrice[i]);
    }
    free(matrice);

    return 0;
}

EDIT: If you really want to use getline() , here's a version of your original program that'll work:

#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>
#include <ncurses.h>

int main(int argc, char const *argv[]) {
    size_t nbytes = 0;
    int i = 0, j = 0;

    if ( argc < 2 ) {
        fputs("You must specify a file name!", stderr);
        return EXIT_FAILURE;
    }

    FILE *lab = fopen(argv[1], "r");
    if ( lab == NULL ) {
        fputs("Couldn't open file!", stderr);
        return EXIT_FAILURE;
    }

    char **matrice = malloc(sizeof(char *) * 51);
    if ( matrice == NULL ) {
        fputs("Couldn't allocate memory!", stderr);
        return EXIT_FAILURE;
    }

    for ( j = 0; j < 51; ++j ) {
        matrice[j] = NULL;
    }

    while ( i < 50 &&
            (getline(&matrice[i], &nbytes, lab) != -1) ) {
        i++;
    }

    if ( i == 0 ) {
        fputs("File was empty.", stderr);
        free(matrice[0]);
        free(matrice);

        return EXIT_FAILURE;
    }

    printf("%s", matrice[0]);
    getchar();
    initscr();                  /* Start curses mode        */
    cbreak();                   /* Line buffering disabled  */
    keypad(stdscr, TRUE);       /* We get F1, F2 etc..      */
    noecho();                   /* Don't echo() while we do getch */
    printw(matrice[0]);
    printw("dummy line\n");
    refresh();
    getch();
    endwin();

    for ( j = 0; j <= i; ++j ) {
        free(matrice[j]);
    }
    free(matrice);

    return EXIT_SUCCESS;
}

but allocating your own memory and using fgets() is better, there's no call for using non-standard extensions when there's a perfectly good standard way of doing it, even if you're using a third-party library like ncurses to begin with.