Program crashed after one line input. How to fix?

-3

I have made a program of getline function of mine. Which takes input till a 'n' is encountered and shifts to the next input. Also I have used pointer arrays here to store the string inputs, but the program crashes after the first string input. What's the problem?

This is the code of the program. I have tried to debug it but it but I can't find the problem here.

#include<stdio.h>

#include<stdlib.h>



void getline2(char *s)

{

    char c;

    while((c=getchar())!='n')

    {

        *s=c;

        s++;

    }

    *s='';

}



int main()

{

    char *lines[3];

    int i=0;

    while(i<3)

    {

        getline2(lines[i]);

        i++;

    }

    for (i = 0; i < 3; i++)

    {

        printf("n%s", lines[i]);

    }

    return 0;

}

When I input the first line after pressing the enter the program crashes.

edited Jan 2 at 7:30

Sourav Ghosh

111k15131190

asked Jan 2 at 6:48

theviralv

5

You have declared an array of pointers but have not allocated memory for the pointers. Your code has undefined behavior because of that.

– R Sahu
Jan 2 at 6:50

1

Curious: who or what text suggested putting a "n" at the start of "n%s"?

– chux
Jan 2 at 6:52

1

Read How to debug small programs. You really should be able to find such bugs by yourself.

– Basile Starynkevitch
Jan 2 at 7:03

1

If the printf loop is not relevant, then it should be removed from the Minimal, Complete, and Verifiable example.

– Werner Henze
Jan 2 at 7:07

1

@chux I disagree. It crashes prior to printf already. The while loop in main is probably noise too. getline2(lines[0]) would have sufficed to produce the crash.

– Antti Haapala
Jan 2 at 8:30

|
show 3 more comments

-3

This is the code of the program. I have tried to debug it but it but I can't find the problem here.

#include<stdio.h>

#include<stdlib.h>



void getline2(char *s)

{

    char c;

    while((c=getchar())!='n')

    {

        *s=c;

        s++;

    }

    *s='';

}



int main()

{

    char *lines[3];

    int i=0;

    while(i<3)

    {

        getline2(lines[i]);

        i++;

    }

    for (i = 0; i < 3; i++)

    {

        printf("n%s", lines[i]);

    }

    return 0;

}

When I input the first line after pressing the enter the program crashes.

edited Jan 2 at 7:30

Sourav Ghosh

111k15131190

asked Jan 2 at 6:48

theviralv

5

You have declared an array of pointers but have not allocated memory for the pointers. Your code has undefined behavior because of that.

– R Sahu
Jan 2 at 6:50

1

Curious: who or what text suggested putting a "n" at the start of "n%s"?

– chux
Jan 2 at 6:52

1

Read How to debug small programs. You really should be able to find such bugs by yourself.

– Basile Starynkevitch
Jan 2 at 7:03

1

If the printf loop is not relevant, then it should be removed from the Minimal, Complete, and Verifiable example.

– Werner Henze
Jan 2 at 7:07

1

@chux I disagree. It crashes prior to printf already. The while loop in main is probably noise too. getline2(lines[0]) would have sufficed to produce the crash.

– Antti Haapala
Jan 2 at 8:30

|
show 3 more comments

-3

This is the code of the program. I have tried to debug it but it but I can't find the problem here.

#include<stdio.h>

#include<stdlib.h>



void getline2(char *s)

{

    char c;

    while((c=getchar())!='n')

    {

        *s=c;

        s++;

    }

    *s='';

}



int main()

{

    char *lines[3];

    int i=0;

    while(i<3)

    {

        getline2(lines[i]);

        i++;

    }

    for (i = 0; i < 3; i++)

    {

        printf("n%s", lines[i]);

    }

    return 0;

}

When I input the first line after pressing the enter the program crashes.

edited Jan 2 at 7:30

Sourav Ghosh

111k15131190

asked Jan 2 at 6:48

theviralv

This is the code of the program. I have tried to debug it but it but I can't find the problem here.

#include<stdio.h>

#include<stdlib.h>



void getline2(char *s)

{

    char c;

    while((c=getchar())!='n')

    {

        *s=c;

        s++;

    }

    *s='';

}



int main()

{

    char *lines[3];

    int i=0;

    while(i<3)

    {

        getline2(lines[i]);

        i++;

    }

    for (i = 0; i < 3; i++)

    {

        printf("n%s", lines[i]);

    }

    return 0;

}

When I input the first line after pressing the enter the program crashes.

c pointers getline

edited Jan 2 at 7:30

Sourav Ghosh

111k15131190

asked Jan 2 at 6:48

theviralv

edited Jan 2 at 7:30

Sourav Ghosh

111k15131190

asked Jan 2 at 6:48

theviralv

edited Jan 2 at 7:30

Sourav Ghosh

111k15131190

edited Jan 2 at 7:30

Sourav Ghosh

111k15131190

edited Jan 2 at 7:30

Sourav Ghosh

111k15131190

asked Jan 2 at 6:48

theviralv

asked Jan 2 at 6:48

theviralv

asked Jan 2 at 6:48

theviralv

5

You have declared an array of pointers but have not allocated memory for the pointers. Your code has undefined behavior because of that.

– R Sahu
Jan 2 at 6:50

1

Curious: who or what text suggested putting a "n" at the start of "n%s"?

– chux
Jan 2 at 6:52

1

Read How to debug small programs. You really should be able to find such bugs by yourself.

– Basile Starynkevitch
Jan 2 at 7:03

1

If the printf loop is not relevant, then it should be removed from the Minimal, Complete, and Verifiable example.

– Werner Henze
Jan 2 at 7:07

1

@chux I disagree. It crashes prior to printf already. The while loop in main is probably noise too. getline2(lines[0]) would have sufficed to produce the crash.

– Antti Haapala
Jan 2 at 8:30

|
show 3 more comments

5

You have declared an array of pointers but have not allocated memory for the pointers. Your code has undefined behavior because of that.

– R Sahu
Jan 2 at 6:50

1

Curious: who or what text suggested putting a "n" at the start of "n%s"?

– chux
Jan 2 at 6:52

1

Read How to debug small programs. You really should be able to find such bugs by yourself.

– Basile Starynkevitch
Jan 2 at 7:03

1

If the printf loop is not relevant, then it should be removed from the Minimal, Complete, and Verifiable example.

– Werner Henze
Jan 2 at 7:07

1

@chux I disagree. It crashes prior to printf already. The while loop in main is probably noise too. getline2(lines[0]) would have sufficed to produce the crash.

– Antti Haapala
Jan 2 at 8:30

You have declared an array of pointers but have not allocated memory for the pointers. Your code has undefined behavior because of that.

– R Sahu
Jan 2 at 6:50

Curious: who or what text suggested putting a "n" at the start of "n%s"?

– chux
Jan 2 at 6:52

Read How to debug small programs. You really should be able to find such bugs by yourself.

– Basile Starynkevitch
Jan 2 at 7:03

If the printf loop is not relevant, then it should be removed from the Minimal, Complete, and Verifiable example.

– Werner Henze
Jan 2 at 7:07

@chux I disagree. It crashes prior to printf already. The while loop in main is probably noise too. getline2(lines[0]) would have sufficed to produce the crash.

– Antti Haapala
Jan 2 at 8:30

|
show 3 more comments

2 Answers
2

active

oldest

votes

In your code, char *lines[3]; defines an array of char pointers. The pointers themselves do not point to any valid memory automatically. Unless initialized properly, attempt to use (or de-reference) them would lead to undefined behavior.

There are two common approach of achieving what you want (based on your requirement):

Allocate a size at compile time and length-limit your input [i.e., pass the size of the buffer as a function argument, like fgets()]

Allocate memory at run time (allocator functions, malloc() and family) and resize based on the input length.

edited Jan 2 at 7:02

answered Jan 2 at 6:51

Sourav Ghosh

111k15131190

add a comment |

In addition to supplying a char* which points to valid memory (as well suggested by others), getline2() has other weaknesses to address.

Unknown size

getline2() does not know how many characters can be saved. Suggest accepting a size parameter and adjust code to prevent overfilling s.

// void getline2(char *s)

void getline2(char *s, size_t sz)

Infinite loop on EOF

When stdin is closed or a rare input error occurs, getchar() can perpetual return EOF and never exit the loop.

257 values do not fit in char

int fgetc() returns values in the range of unsigned char and EOF. Use int c; and test loop for c != 'n' && c != EOF

// char c;

// while((c=getchar())!='n')

int c;

while((c=getchar())!='n' && c != EOF)

answered Jan 2 at 7:34

chux

84.3k874154

add a comment |

Your Answer

StackExchange.ifUsing("editor", function () {
StackExchange.using("externalEditor", function () {
StackExchange.using("snippets", function () {
StackExchange.snippets.init();
});
});
}, "code-snippets");

StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "1"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});

function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});

}
});

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f54002322%2fprogram-crashed-after-one-line-input-how-to-fix%23new-answer', 'question_page');
}
);

Post as a guest

Name

Required, but never shown

2 Answers
2

active

oldest

votes

2 Answers
2

active

oldest

votes

There are two common approach of achieving what you want (based on your requirement):

Allocate a size at compile time and length-limit your input [i.e., pass the size of the buffer as a function argument, like fgets()]

Allocate memory at run time (allocator functions, malloc() and family) and resize based on the input length.

edited Jan 2 at 7:02

answered Jan 2 at 6:51

Sourav Ghosh

111k15131190

add a comment |

There are two common approach of achieving what you want (based on your requirement):

Allocate a size at compile time and length-limit your input [i.e., pass the size of the buffer as a function argument, like fgets()]

Allocate memory at run time (allocator functions, malloc() and family) and resize based on the input length.

edited Jan 2 at 7:02

answered Jan 2 at 6:51

Sourav Ghosh

111k15131190

add a comment |

There are two common approach of achieving what you want (based on your requirement):

Allocate a size at compile time and length-limit your input [i.e., pass the size of the buffer as a function argument, like fgets()]

Allocate memory at run time (allocator functions, malloc() and family) and resize based on the input length.

edited Jan 2 at 7:02

answered Jan 2 at 6:51

Sourav Ghosh

111k15131190

There are two common approach of achieving what you want (based on your requirement):

Allocate a size at compile time and length-limit your input [i.e., pass the size of the buffer as a function argument, like fgets()]

Allocate memory at run time (allocator functions, malloc() and family) and resize based on the input length.

edited Jan 2 at 7:02

answered Jan 2 at 6:51

Sourav Ghosh

111k15131190

edited Jan 2 at 7:02

answered Jan 2 at 6:51

Sourav Ghosh

111k15131190

answered Jan 2 at 6:51

Sourav Ghosh

111k15131190

answered Jan 2 at 6:51

Sourav Ghosh

111k15131190

add a comment |

In addition to supplying a char* which points to valid memory (as well suggested by others), getline2() has other weaknesses to address.

Unknown size

getline2() does not know how many characters can be saved. Suggest accepting a size parameter and adjust code to prevent overfilling s.

// void getline2(char *s)

void getline2(char *s, size_t sz)

Infinite loop on EOF

When stdin is closed or a rare input error occurs, getchar() can perpetual return EOF and never exit the loop.

257 values do not fit in char

int fgetc() returns values in the range of unsigned char and EOF. Use int c; and test loop for c != 'n' && c != EOF

// char c;

// while((c=getchar())!='n')

int c;

while((c=getchar())!='n' && c != EOF)

answered Jan 2 at 7:34

chux

84.3k874154

add a comment |

In addition to supplying a char* which points to valid memory (as well suggested by others), getline2() has other weaknesses to address.

Unknown size

getline2() does not know how many characters can be saved. Suggest accepting a size parameter and adjust code to prevent overfilling s.

// void getline2(char *s)

void getline2(char *s, size_t sz)

Infinite loop on EOF

When stdin is closed or a rare input error occurs, getchar() can perpetual return EOF and never exit the loop.

257 values do not fit in char

int fgetc() returns values in the range of unsigned char and EOF. Use int c; and test loop for c != 'n' && c != EOF

// char c;

// while((c=getchar())!='n')

int c;

while((c=getchar())!='n' && c != EOF)

answered Jan 2 at 7:34

chux

84.3k874154

add a comment |

In addition to supplying a char* which points to valid memory (as well suggested by others), getline2() has other weaknesses to address.

Unknown size

getline2() does not know how many characters can be saved. Suggest accepting a size parameter and adjust code to prevent overfilling s.

// void getline2(char *s)

void getline2(char *s, size_t sz)

Infinite loop on EOF

When stdin is closed or a rare input error occurs, getchar() can perpetual return EOF and never exit the loop.

257 values do not fit in char

int fgetc() returns values in the range of unsigned char and EOF. Use int c; and test loop for c != 'n' && c != EOF

// char c;

// while((c=getchar())!='n')

int c;

while((c=getchar())!='n' && c != EOF)

answered Jan 2 at 7:34

chux

84.3k874154

In addition to supplying a char* which points to valid memory (as well suggested by others), getline2() has other weaknesses to address.

Unknown size

getline2() does not know how many characters can be saved. Suggest accepting a size parameter and adjust code to prevent overfilling s.

// void getline2(char *s)

void getline2(char *s, size_t sz)

Infinite loop on EOF

When stdin is closed or a rare input error occurs, getchar() can perpetual return EOF and never exit the loop.

257 values do not fit in char

int fgetc() returns values in the range of unsigned char and EOF. Use int c; and test loop for c != 'n' && c != EOF

// char c;

// while((c=getchar())!='n')

int c;

while((c=getchar())!='n' && c != EOF)

answered Jan 2 at 7:34

chux

84.3k874154

answered Jan 2 at 7:34

chux

84.3k874154

answered Jan 2 at 7:34

chux

84.3k874154

answered Jan 2 at 7:34

chux

84.3k874154

add a comment |

draft saved

draft discarded

Thanks for contributing an answer to Stack Overflow!

Please be sure to answer the question. Provide details and share your research!

But avoid …

Asking for help, clarification, or responding to other answers.

Making statements based on opinion; back them up with references or personal experience.

To learn more, see our tips on writing great answers.

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Name

Required, but never shown

Name

Required, but never shown

This page is only for reference, If you need detailed information, please check here

Search This Blog

Ufyukyu