C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  scanf() quesion?          C++Talk.NET Forum Index -> C Language View previous topic :: View next topic   Author Message guoliang Guest Posted: Fri May 11, 2007 9:12 am    Post subject: scanf() quesion? help: #include<stdio.h> int main(void) { int a; char b; printf("int="); scanf("%d",&a); fflush(stdin); printf("char="); scanf("%c",&b); printf("a=%d, str=%c\n",a,b); return 0; } input:1 and return; output:char=a=1, b= how can i assigment :a=1,b='x'? Back to top Richard Heathfield Guest Posted: Fri May 11, 2007 9:12 am    Post subject: Re: scanf() quesion? guoliang said: Quote: help: #include<stdio.h int main(void) { int a; char b; printf("int="); If you want the prompt to appear before the program blocks for input, ensure that this happens, either by completing the line or by flushing the stream with fflush(stdout); this is because the standard output stream is typically line-buffered. Quote: scanf("%d",&a); When you call scanf, you are asking for a resource (in this case, information from the standard input stream). Whenever you ask for a resource, the possibility exists that you don't get what you ask for, and you should anticipate and deal with this possibility. Quote: fflush(stdin); The behaviour of fflush is defined only for streams open for output or update. Since stdin is not such a stream, you invoke undefined behaviour. Quote: printf("char="); scanf("%c",&b); printf("a=%d, str=%c\n",a,b); return 0; } input:1 and return; output:char=a=1, b= The only reason this isn't impossible is that the fflush(stdin) rendered the behaviour of your program undefined. Quote: how can i assigment :a=1,b='x'? a = 1; b = 'x'; -- Richard Heathfield "Usenet is a strange place" - dmr 29/7/1999 http://www.cpax.org.uk email: rjh at the above domain, - www. Back to top Richard Heathfield Guest Posted: Sat May 12, 2007 9:11 am    Post subject: Re: scanf() quesion? Chris Torek said: Quote: If you have access to a Linux or Unix box, try: ./prog | tee save_output and observe the fact that printf() output does not appear as desired unless the fflush(stdout) calls are in place. Ouch! A lesson learned. -- Richard Heathfield "Usenet is a strange place" - dmr 29/7/1999 http://www.cpax.org.uk email: rjh at the above domain, - www. Back to top Richard Heathfield Guest Posted: Mon May 14, 2007 9:12 am    Post subject: Re: scanf() quesion? guru.jois (AT) gmail (DOT) com said: Quote: On May 11, 12:47 pm, Richard Heathfield <r...@see.sig.invalid> wrote: guoliang said: snip Quote: scanf("%d",&a); When you call scanf, you are asking for a resource (in this case, information from the standard input stream). Whenever you ask for a resource, the possibility exists that you don't get what you ask for, and you should anticipate and deal with this possibility. <snip> Quote: or do this scanf (" %c", &c); // space before %c.. See above. I sometimes think the ability to read is becoming unfashionable. -- Richard Heathfield "Usenet is a strange place" - dmr 29/7/1999 http://www.cpax.org.uk email: rjh at the above domain, - www. Back to top guru.jois@gmail.com Guest Posted: Mon May 14, 2007 9:12 am    Post subject: Re: scanf() quesion? On May 11, 12:47 pm, Richard Heathfield <r...@see.sig.invalid> wrote: Quote: guoliang said: help: #include<stdio.h int main(void) { int a; char b; printf("int="); If you want the prompt to appear before the program blocks for input, ensure that this happens, either by completing the line or by flushing the stream with fflush(stdout); this is because the standard output stream is typically line-buffered. scanf("%d",&a); When you call scanf, you are asking for a resource (in this case, information from the standard input stream). Whenever you ask for a resource, the possibility exists that you don't get what you ask for, and you should anticipate and deal with this possibility. fflush(stdin); The behaviour of fflush is defined only for streams open for output or update. Since stdin is not such a stream, you invoke undefined behaviour. printf("char="); scanf("%c",&b); printf("a=%d, str=%c\n",a,b); return 0; } input:1 and return; output:char=a=1, b= The only reason this isn't impossible is that the fflush(stdin) rendered the behaviour of your program undefined. how can i assigment :a=1,b='x'? a = 1; b = 'x'; -- Richard Heathfield "Usenet is a strange place" - dmr 29/7/1999http://www.cpax.org.uk email: rjh at the above domain, - www. or do this scanf (" %c", &c); // space before %c.. 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