Reading file of 1's and 0's one at a time

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0
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In C++ I am trying to read from the following file into an array:

I am using the following to put each int into an array:

 X = (int* )malloc(n*n*sizeof(int));
 for (int i = 0; i<(n*n); i++)
 j = read.get();
 if (isdigit(j))
 *(X+i) = j - '0';

But when I output to array to a file I get the following output:

And I don't believe there is anything wrong with how I am outputting my array:

for (int i = 0; i<(n*n); i++)
 write << *(X+i);
 if (((1+i) % n) == 0)
 write << endl;

I tried reading with the following but it didn't seem to work:

for (int i = 0; i<(n*n); i++)
 
 read >> *(X+i);

edited Nov 9 at 23:37

Galik

33.1k34674

asked Nov 9 at 23:36

bob

2

Don't use malloc() in C++, use new. Even better, use std::vector instead of C-style arrays.
– Barmar
Nov 9 at 23:38

It is not recommended to use malloc() in C++. You should generally use new or (better) a container like std::vector or std::array.
– Galik
Nov 9 at 23:38

The problem is in your read loop, on handling (or not handling) non-digits. The corresponding int in the buffer is left uninitialised, but the writing code assumes something is stored there. The result (accessing an uninitialised int in the write loop) is undefined behaviour.
– Peter
Nov 9 at 23:42

add a comment |

up vote
0
down vote

favorite

In C++ I am trying to read from the following file into an array:

I am using the following to put each int into an array:

 X = (int* )malloc(n*n*sizeof(int));
 for (int i = 0; i<(n*n); i++)
 j = read.get();
 if (isdigit(j))
 *(X+i) = j - '0';

But when I output to array to a file I get the following output:

And I don't believe there is anything wrong with how I am outputting my array:

for (int i = 0; i<(n*n); i++)
 write << *(X+i);
 if (((1+i) % n) == 0)
 write << endl;

I tried reading with the following but it didn't seem to work:

for (int i = 0; i<(n*n); i++)
 
 read >> *(X+i);

edited Nov 9 at 23:37

Galik

33.1k34674

asked Nov 9 at 23:36

bob

2

Don't use malloc() in C++, use new. Even better, use std::vector instead of C-style arrays.
– Barmar
Nov 9 at 23:38

It is not recommended to use malloc() in C++. You should generally use new or (better) a container like std::vector or std::array.
– Galik
Nov 9 at 23:38

The problem is in your read loop, on handling (or not handling) non-digits. The corresponding int in the buffer is left uninitialised, but the writing code assumes something is stored there. The result (accessing an uninitialised int in the write loop) is undefined behaviour.
– Peter
Nov 9 at 23:42

add a comment |

up vote
0
down vote

favorite

In C++ I am trying to read from the following file into an array:

I am using the following to put each int into an array:

 X = (int* )malloc(n*n*sizeof(int));
 for (int i = 0; i<(n*n); i++)
 j = read.get();
 if (isdigit(j))
 *(X+i) = j - '0';

But when I output to array to a file I get the following output:

And I don't believe there is anything wrong with how I am outputting my array:

for (int i = 0; i<(n*n); i++)
 write << *(X+i);
 if (((1+i) % n) == 0)
 write << endl;

I tried reading with the following but it didn't seem to work:

for (int i = 0; i<(n*n); i++)
 
 read >> *(X+i);

edited Nov 9 at 23:37

Galik

33.1k34674

asked Nov 9 at 23:36

bob

In C++ I am trying to read from the following file into an array:

I am using the following to put each int into an array:

 X = (int* )malloc(n*n*sizeof(int));
 for (int i = 0; i<(n*n); i++)
 j = read.get();
 if (isdigit(j))
 *(X+i) = j - '0';

But when I output to array to a file I get the following output:

And I don't believe there is anything wrong with how I am outputting my array:

for (int i = 0; i<(n*n); i++)
 write << *(X+i);
 if (((1+i) % n) == 0)
 write << endl;

I tried reading with the following but it didn't seem to work:

for (int i = 0; i<(n*n); i++)
 
 read >> *(X+i);

c++ file

edited Nov 9 at 23:37

Galik

33.1k34674

asked Nov 9 at 23:36

bob

edited Nov 9 at 23:37

Galik

33.1k34674

asked Nov 9 at 23:36

bob

edited Nov 9 at 23:37

Galik

33.1k34674

edited Nov 9 at 23:37

Galik

33.1k34674

edited Nov 9 at 23:37

Galik

33.1k34674

asked Nov 9 at 23:36

bob

asked Nov 9 at 23:36

bob

asked Nov 9 at 23:36

bob

2

Don't use malloc() in C++, use new. Even better, use std::vector instead of C-style arrays.
– Barmar
Nov 9 at 23:38

It is not recommended to use malloc() in C++. You should generally use new or (better) a container like std::vector or std::array.
– Galik
Nov 9 at 23:38

The problem is in your read loop, on handling (or not handling) non-digits. The corresponding int in the buffer is left uninitialised, but the writing code assumes something is stored there. The result (accessing an uninitialised int in the write loop) is undefined behaviour.
– Peter
Nov 9 at 23:42

add a comment |

2

Don't use malloc() in C++, use new. Even better, use std::vector instead of C-style arrays.
– Barmar
Nov 9 at 23:38

It is not recommended to use malloc() in C++. You should generally use new or (better) a container like std::vector or std::array.
– Galik
Nov 9 at 23:38

The problem is in your read loop, on handling (or not handling) non-digits. The corresponding int in the buffer is left uninitialised, but the writing code assumes something is stored there. The result (accessing an uninitialised int in the write loop) is undefined behaviour.
– Peter
Nov 9 at 23:42

Don't use malloc() in C++, use new. Even better, use std::vector instead of C-style arrays.
– Barmar
Nov 9 at 23:38

It is not recommended to use malloc() in C++. You should generally use new or (better) a container like std::vector or std::array.
– Galik
Nov 9 at 23:38

The problem is in your read loop, on handling (or not handling) non-digits. The corresponding int in the buffer is left uninitialised, but the writing code assumes something is stored there. The result (accessing an uninitialised int in the write loop) is undefined behaviour.
– Peter
Nov 9 at 23:42

add a comment |

1 Answer
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up vote
4
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The problem is that you're incrementing i even when isdigit(j) is false. So you're leaving the array elements corresponding to the newlines in the file uninitialized, and also not reading all the digits because you're counting the newlines. You need to put the increment inside the if.

for (int i = 0; i < n*n; ) 
 char j = read.get();
 if (isdigit(j)) 
 X[i++] = j - '0';

BTW, if you're using a pointer as an array, use array syntax X[index] rather than *(X+index). It makes the intent clearer.

answered Nov 9 at 23:42

Barmar

413k34239339

add a comment |

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up vote
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down vote

for (int i = 0; i < n*n; ) 
 char j = read.get();
 if (isdigit(j)) 
 X[i++] = j - '0';

BTW, if you're using a pointer as an array, use array syntax X[index] rather than *(X+index). It makes the intent clearer.

answered Nov 9 at 23:42

Barmar

413k34239339

add a comment |

up vote
4
down vote

for (int i = 0; i < n*n; ) 
 char j = read.get();
 if (isdigit(j)) 
 X[i++] = j - '0';

BTW, if you're using a pointer as an array, use array syntax X[index] rather than *(X+index). It makes the intent clearer.

answered Nov 9 at 23:42

Barmar

413k34239339

add a comment |

up vote
4
down vote

for (int i = 0; i < n*n; ) 
 char j = read.get();
 if (isdigit(j)) 
 X[i++] = j - '0';

BTW, if you're using a pointer as an array, use array syntax X[index] rather than *(X+index). It makes the intent clearer.

answered Nov 9 at 23:42

Barmar

413k34239339

for (int i = 0; i < n*n; ) 
 char j = read.get();
 if (isdigit(j)) 
 X[i++] = j - '0';

BTW, if you're using a pointer as an array, use array syntax X[index] rather than *(X+index). It makes the intent clearer.

answered Nov 9 at 23:42

Barmar

413k34239339

answered Nov 9 at 23:42

Barmar

413k34239339

answered Nov 9 at 23:42

Barmar

413k34239339

answered Nov 9 at 23:42

Barmar

413k34239339

add a comment |

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