arrays - Trying to understand the usage of multidimension dynamic fields in C -
i'm trying learn c @ moment , have encountered task cannot solve on own. simple minesweeper implementation.
short description program should do: gets input files via command line, opens them 1 @ time, creates minesweeper field each , if multiple files opened program saves them formatted in 1 file. don't want format them 1 beneath other, want use dynamic 2 dimensional array, matrix expands without losing saved mines.
each input file has same build:
3\t5\n 0\t3\n 3\t7\n ... the first line indicates size of n x m matrix , following lines coordinates of mines.
here code far:
#include <unistd.h> #include <stdlib.h> #include <stdio.h> #include <string.h> typedef struct game{ int n; int field[]; }game; int read_files(char **input, int length); int make_field(char *input, int i, int *ptr); void increment(int i, int j, game); int is_inside_bounds(int i, int j, game); void free_field(); void safe_field(); int main(int argc, char **argv){ read_files(argv, argc); return 0; } //read_files reads files given programm via commandline int read_files(char **input, int length){ int i= 1; char string[20]; //input goes via fgets int filecount = 0; //counts amount of files int fieldptr[100]; // int array purpose of memorizing size of gamefields create int j = 0; (; i< length-1; i++){ file *in; if(!(in = fopen(input[i], "r"))){ fprintf(stderr, "file not found.\n"); err = 2; return err; } while (fgets(string,20,in)){ make_field(string, filecount, fieldptr); //gives relevan info make_field function j++; } fclose(in); filecount++; } return 0; } int make_field(char *string, int file, int *fieldptr){ struct g = null;//this problem int g.field = null;//this char delimiter[] = "\t\n"; //the input file cuts chars \n , \t char *ptr; //needed strtok file= file * 2; //this used filehandling ptr = strtok(string, delimiter); int = atoi(ptr); //cast int have gamefield size int ptr = strtok(null, delimiter); int b = atoi(ptr); //cast int have gamefield size int if (fieldptr[file] == 0 && file == 0){//init field fieldptr[0] = a; //memorize first call fieldptr [1] = b; g.field = malloc(a * sizeof(int*)); if (null == field){ fprintf(stderr, "memory error.\n"); return 3; } for(int j = 0; j < a; j++){ g.field[j] = malloc(b * sizeof(int)); if(null==g.field[j]){ allocated fprintf(stderr, "memory error.\n"); return 3; } } }else if (fieldptr[file] == 0 && file != 0){ //if first line , not first file field = realloc(g.field, * sizeof(int*)); if (null == field){ fprintf(stderr, "memory error.\n"); return 3; } for(int j = 0; j < a; j++){ field[j] = realloc(field[j], b * sizeof(int)); if(null==g.field[j]) fprintf(stderr, "memory error.\n"); return 3; } } fieldptr[file] = a; //filehandling memory fieldptr[file+1] = b; }else if(fieldptr[file] != 0 && file == 0){ //fill mines +indicators array g.field[a][b] = -1; int m; (m = -1; m <= 1; m++) { int n; (n = -1; n <= 1; n++) { increment(a + m, (fieldptr[file+b]) + n, g); } } }else if (fieldptr[file] != 0 && file != 0){ //fill mines +indicators bigger array g.field[a][fieldptr[file+b]] = -1; int m; (m = -1; m <= 1; m++) { int n; (n = -1; n <= 1; n++) { increment(a + m, (fieldptr[file+b]) + n, g); } } } return field; //not sure return yet } void increment(int i, int j, game *g) { //increments neighbours of minefield if (is_inside_bounds(i, j, g) && field[i][j] != -1) { ++g.field[i][j]; } } int is_inside_bounds(int i, int j, game *g) { //checks if access of increment inside array int nlines = sizeof(g.field) / sizeof(g.field[0][0]); int ncolumns = sizeof(g.field[0]) / sizeof(field[0][0]); return >= 0 && < nlines && j >=0 && j < ncolumns; } coming java, in eyes should work, don't how c works multidim arrays. can point me right direction?
edit:
gcc has following output:
error: invalid use of flexible array member g.field = realloc(g.field, * sizeof(int*)); in function ‘increment’: note: abi of passing struct flexible array member has changed in gcc 4.4 void increment(int i, int j, game g) { so problem don't know how declare , use array right way.
struct g = null;//this problem int g.field = null;//this you right, problem
1) mean game g instead of struct g
2) can not use null without pointer:
game *g = null; /* ok */ 3) can not access member (g.field) of uninitialized struct (g)
more problems:
g.field = malloc(a * sizeof(int*)); you can not use malloc flexible array member, need reserve space whole struct including size of flexible array member:
game *g = malloc(sizeof(*g) + (n * sizeof(int))); or better yet
game *g = malloc(sizeof(*g) + (n * sizeof(g->field[0]))); note sizeof(int) instead of sizeof(int *), want reserve space n ints not n pointers ints
or change field
typedef struct game { int n; int *field; } game; in order use malloc member directly.
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