printf wrong output when reversing a string [duplicate]

-1

This question already has an answer here:

Reversing a string literal in C with pointers [duplicate]

1 answer

so this is the code for reversing a string

#include<stdio.h>



char* function(char *);

int main()

{   

   char a="computer";

   printf("%s", function(a));

   return 0;

}



char* function(char *p)

{

   int l,i;

   char t;

   for (l=0;*(p+l)!='';l++);

   for(i=0; i<(l/2) ; i++)

    {

        t=*(p+i);

        *(p+i)=*(p+l-1-i);

        *(p+l-1-i)=t;

    }



   return (p);

}

but if i change printf("%s", function(a)); in the main body to

printf("%s", function("computer"));

there is no output (the output is blank) in dev c++.... but it gives the desired output in turbo c++ even with this change....why is that?

asked Nov 20 '18 at 20:51

Anas Aziz

347

marked as duplicate by WhozCraig c
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Nov 20 '18 at 20:58

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

2

Your program invokes undefined behavior when you write to a string literal with the second version. There are at least a thousand duplicates of this issue on this site, but the title's rarely reflect the actual issue, and are so divergent they're surprisingly difficult to find. Turbo C++ is probably older than you are, so get a modern compiler and turn up your warnings to pedantic levels.

– WhozCraig
Nov 20 '18 at 20:57

1

Exact duplicate of Reversing a string literal in C with pointers

– usr2564301
Nov 20 '18 at 20:57

1

Tip: Don't use l and 1 and i in arithmetic expressions.

– Tim Randall
Nov 20 '18 at 20:58

1

@TimRandall because we can get it mixed up right?

– Anas Aziz
Nov 20 '18 at 21:01

@AnasAziz Yes, it's difficult to read. Personally I don't like to use single letter variable names, except in for loops or cases where the meaning is super-obvious. I like to use one or two word names where possible.

– Tim Randall
Nov 20 '18 at 21:05

add a comment |

-1

This question already has an answer here:

Reversing a string literal in C with pointers [duplicate]

1 answer

so this is the code for reversing a string

#include<stdio.h>



char* function(char *);

int main()

{   

   char a="computer";

   printf("%s", function(a));

   return 0;

}



char* function(char *p)

{

   int l,i;

   char t;

   for (l=0;*(p+l)!='';l++);

   for(i=0; i<(l/2) ; i++)

    {

        t=*(p+i);

        *(p+i)=*(p+l-1-i);

        *(p+l-1-i)=t;

    }



   return (p);

}

but if i change printf("%s", function(a)); in the main body to

printf("%s", function("computer"));

there is no output (the output is blank) in dev c++.... but it gives the desired output in turbo c++ even with this change....why is that?

asked Nov 20 '18 at 20:51

Anas Aziz

347

marked as duplicate by WhozCraig c
Users with the c badge can single-handedly close c questions as duplicates and reopen them as needed.

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Nov 20 '18 at 20:58

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

2

Your program invokes undefined behavior when you write to a string literal with the second version. There are at least a thousand duplicates of this issue on this site, but the title's rarely reflect the actual issue, and are so divergent they're surprisingly difficult to find. Turbo C++ is probably older than you are, so get a modern compiler and turn up your warnings to pedantic levels.

– WhozCraig
Nov 20 '18 at 20:57

1

Exact duplicate of Reversing a string literal in C with pointers

– usr2564301
Nov 20 '18 at 20:57

1

Tip: Don't use l and 1 and i in arithmetic expressions.

– Tim Randall
Nov 20 '18 at 20:58

1

@TimRandall because we can get it mixed up right?

– Anas Aziz
Nov 20 '18 at 21:01

@AnasAziz Yes, it's difficult to read. Personally I don't like to use single letter variable names, except in for loops or cases where the meaning is super-obvious. I like to use one or two word names where possible.

– Tim Randall
Nov 20 '18 at 21:05

add a comment |

-1

This question already has an answer here:

Reversing a string literal in C with pointers [duplicate]

1 answer

so this is the code for reversing a string

#include<stdio.h>



char* function(char *);

int main()

{   

   char a="computer";

   printf("%s", function(a));

   return 0;

}



char* function(char *p)

{

   int l,i;

   char t;

   for (l=0;*(p+l)!='';l++);

   for(i=0; i<(l/2) ; i++)

    {

        t=*(p+i);

        *(p+i)=*(p+l-1-i);

        *(p+l-1-i)=t;

    }



   return (p);

}

but if i change printf("%s", function(a)); in the main body to

printf("%s", function("computer"));

there is no output (the output is blank) in dev c++.... but it gives the desired output in turbo c++ even with this change....why is that?

asked Nov 20 '18 at 20:51

Anas Aziz

347

This question already has an answer here:

Reversing a string literal in C with pointers [duplicate]

1 answer

so this is the code for reversing a string

#include<stdio.h>



char* function(char *);

int main()

{   

   char a="computer";

   printf("%s", function(a));

   return 0;

}



char* function(char *p)

{

   int l,i;

   char t;

   for (l=0;*(p+l)!='';l++);

   for(i=0; i<(l/2) ; i++)

    {

        t=*(p+i);

        *(p+i)=*(p+l-1-i);

        *(p+l-1-i)=t;

    }



   return (p);

}

but if i change printf("%s", function(a)); in the main body to

printf("%s", function("computer"));

there is no output (the output is blank) in dev c++.... but it gives the desired output in turbo c++ even with this change....why is that?

This question already has an answer here:

Reversing a string literal in C with pointers [duplicate]

1 answer

c string pointers printf reverse

asked Nov 20 '18 at 20:51

Anas Aziz

347

asked Nov 20 '18 at 20:51

Anas Aziz

347

asked Nov 20 '18 at 20:51

Anas Aziz

347

asked Nov 20 '18 at 20:51

Anas Aziz

347

asked Nov 20 '18 at 20:51

Anas Aziz

347

marked as duplicate by WhozCraig c
Users with the c badge can single-handedly close c questions as duplicates and reopen them as needed.

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Nov 20 '18 at 20:58

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

marked as duplicate by WhozCraig c
Users with the c badge can single-handedly close c questions as duplicates and reopen them as needed.

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Nov 20 '18 at 20:58

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

2

Your program invokes undefined behavior when you write to a string literal with the second version. There are at least a thousand duplicates of this issue on this site, but the title's rarely reflect the actual issue, and are so divergent they're surprisingly difficult to find. Turbo C++ is probably older than you are, so get a modern compiler and turn up your warnings to pedantic levels.

– WhozCraig
Nov 20 '18 at 20:57

1

Exact duplicate of Reversing a string literal in C with pointers

– usr2564301
Nov 20 '18 at 20:57

1

Tip: Don't use l and 1 and i in arithmetic expressions.

– Tim Randall
Nov 20 '18 at 20:58

1

@TimRandall because we can get it mixed up right?

– Anas Aziz
Nov 20 '18 at 21:01

@AnasAziz Yes, it's difficult to read. Personally I don't like to use single letter variable names, except in for loops or cases where the meaning is super-obvious. I like to use one or two word names where possible.

– Tim Randall
Nov 20 '18 at 21:05

add a comment |

2

Your program invokes undefined behavior when you write to a string literal with the second version. There are at least a thousand duplicates of this issue on this site, but the title's rarely reflect the actual issue, and are so divergent they're surprisingly difficult to find. Turbo C++ is probably older than you are, so get a modern compiler and turn up your warnings to pedantic levels.

– WhozCraig
Nov 20 '18 at 20:57

1

Exact duplicate of Reversing a string literal in C with pointers

– usr2564301
Nov 20 '18 at 20:57

1

Tip: Don't use l and 1 and i in arithmetic expressions.

– Tim Randall
Nov 20 '18 at 20:58

1

@TimRandall because we can get it mixed up right?

– Anas Aziz
Nov 20 '18 at 21:01

@AnasAziz Yes, it's difficult to read. Personally I don't like to use single letter variable names, except in for loops or cases where the meaning is super-obvious. I like to use one or two word names where possible.

– Tim Randall
Nov 20 '18 at 21:05

Your program invokes undefined behavior when you write to a string literal with the second version. There are at least a thousand duplicates of this issue on this site, but the title's rarely reflect the actual issue, and are so divergent they're surprisingly difficult to find. Turbo C++ is probably older than you are, so get a modern compiler and turn up your warnings to pedantic levels.

– WhozCraig
Nov 20 '18 at 20:57

Exact duplicate of Reversing a string literal in C with pointers

– usr2564301
Nov 20 '18 at 20:57

Tip: Don't use l and 1 and i in arithmetic expressions.

– Tim Randall
Nov 20 '18 at 20:58

@TimRandall because we can get it mixed up right?

– Anas Aziz
Nov 20 '18 at 21:01

@AnasAziz Yes, it's difficult to read. Personally I don't like to use single letter variable names, except in for loops or cases where the meaning is super-obvious. I like to use one or two word names where possible.

– Tim Randall
Nov 20 '18 at 21:05

add a comment |

1 Answer
1

active

oldest

votes

Parameter "computer", which you pass to function, is a string literal, and changing/manipulating the contents of a string literal is undefined behaviour. That's what you are experiencing - something undefined.

answered Nov 20 '18 at 20:57

Stephan Lechner

28.1k32143

but then why is it running OK in turboC++ ide?

– Anas Aziz
Nov 21 '18 at 7:34

@Anas: because software from the 1980s did not check if the programmer followed the syntax rules. It just expected them to.

– usr2564301
Nov 21 '18 at 8:32

add a comment |

1 Answer
1

active

oldest

votes

1 Answer
1

active

oldest

votes

answered Nov 20 '18 at 20:57

Stephan Lechner

28.1k32143

but then why is it running OK in turboC++ ide?

– Anas Aziz
Nov 21 '18 at 7:34

@Anas: because software from the 1980s did not check if the programmer followed the syntax rules. It just expected them to.

– usr2564301
Nov 21 '18 at 8:32

add a comment |

answered Nov 20 '18 at 20:57

Stephan Lechner

28.1k32143

but then why is it running OK in turboC++ ide?

– Anas Aziz
Nov 21 '18 at 7:34

@Anas: because software from the 1980s did not check if the programmer followed the syntax rules. It just expected them to.

– usr2564301
Nov 21 '18 at 8:32

add a comment |

answered Nov 20 '18 at 20:57

Stephan Lechner

28.1k32143

answered Nov 20 '18 at 20:57

Stephan Lechner

28.1k32143

answered Nov 20 '18 at 20:57

Stephan Lechner

28.1k32143

answered Nov 20 '18 at 20:57

Stephan Lechner

28.1k32143

answered Nov 20 '18 at 20:57

Stephan Lechner

28.1k32143

but then why is it running OK in turboC++ ide?

– Anas Aziz
Nov 21 '18 at 7:34

@Anas: because software from the 1980s did not check if the programmer followed the syntax rules. It just expected them to.

– usr2564301
Nov 21 '18 at 8:32

add a comment |

but then why is it running OK in turboC++ ide?

– Anas Aziz
Nov 21 '18 at 7:34

@Anas: because software from the 1980s did not check if the programmer followed the syntax rules. It just expected them to.

– usr2564301
Nov 21 '18 at 8:32

but then why is it running OK in turboC++ ide?

– Anas Aziz
Nov 21 '18 at 7:34

@Anas: because software from the 1980s did not check if the programmer followed the syntax rules. It just expected them to.

– usr2564301
Nov 21 '18 at 8:32

add a comment |

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