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• extern and global in c

  - by JPro

  Can anyone please tell me is there any special requirement to use either EXTERN or GLOBAL variables in a C program? I do not see any difference in a program like below, if I change from gloabl to extern. #include <stdio.h> #include <stdlib.h> int myGlobalvar = 10; int main(int argc, char *argv[]) { int myFunc(int); int i; i = 12; myGlobalvar = 100; printf("Value of myGlobalvar is %d , i = %d\n", myGlobalvar, i); i = myFunc(10); printf("Value of passed value : %d\n",i); printf("again Value of myGlobalvar is %d , i = %d\n", myGlobalvar, i); system("PAUSE"); return 0; } int myFunc(int i) { i = 20 + 1000; //extern int myGlobalvar; myGlobalvar = 20000; // printf("Value of passed value : %d",i); return i; } If uncomment extern int myGlobalvar, the value does not change. Is there any correct difference between both? Can anyone please correct me?

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• Iterate through main function in C?

  - by Mohit Deshpande

  Here is my main function: int main(int argc, char **argv) { LoadFile(); Node *temp; char *key; switch (GetUserInput()) { case 1: temp = malloc(sizeof(Node)); printf("\nEnter the key of the new node: "); scanf("%s", temp->key); printf("\nEnter the value of the new node: "); scanf("%s", temp->value); AddNode(temp); free(temp); break; case 2: key = malloc(sizeof(char *)); printf("Enter the key of the node you want to delete: "); scanf("%s", key); DeleteNode(key); free(key); break; case 3: PrintAll(); break; case 4: SaveFile(); break; case 5: return 0; break; default: printf("\nWrong choice!\n"); break; } return 0; } The only problem with it is that after any case statement breaks, the program just exits out. I understand why, but I don't know how to fix it. I want the program to repeat itself each time even after the case statements. Would I just say: main(argc, argv); before every break statement?

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• Strange behavior using getchar() and -O3

  - by Eduardo

  I have these two functions void set_dram_channel_width(int channel_width){ printf("one\n"); getchar(); } void set_dram_transaction_granularity(int cacheline_size){ printf("two\n"); getchar(); } //output: one f //my keyboard input two one f //keyboard input two one f //keyboard input //No more calls Then I change the functions to: void set_dram_channel_width(int channel_width){ printf("one\n"); } void set_dram_transaction_granularity(int cacheline_size){ printf("two\n"); getchar(); } //output one two f //keyboard input //No more calls Both functions are called by an external code, the code for both programs is the same, just changing the getchar() I get those two different outputs. Is this possible or there is something that is really wrong in my code? Thanks This is the output I get with GDB** For the first code (gdb) break mem-dram.c:374 Breakpoint 1 at 0x71c810: file build/ALPHA_FS/mem/dramsim/mem-dram.c, line 374. (gdb) break mem-dram.c:381 Breakpoint 2 at 0x71c7b0: file build/ALPHA_FS/mem/dramsim/mem-dram.c, line 381. (gdb) run -d ./tmp/MyBench2/ one f [Switching to Thread 47368811512112 (LWP 17507)] Breakpoint 1, set_dram_channel_width (channel_width=64) (gdb) c Continuing. two one f Breakpoint 2, set_dram_transaction_granularity (cacheline_size=64) (gdb) c Continuing. Breakpoint 1, set_dram_channel_width (channel_width=8) 374 void set_dram_channel_width(int channel_width){ (gdb) c Continuing. two one f For the second code (gdb) break mem-dram.c:374 Breakpoint 1 at 0x71c7b6: file build/ALPHA_FS/mem/dramsim/mem-dram.c, line 374. (gdb) break mem-dram.c:380 Breakpoint 2 at 0x71c7f0: file build/ALPHA_FS/mem/dramsim/mem-dram.c, line 380. (gdb) run one two f [Switching to Thread 46985688772912 (LWP 17801)] Breakpoint 1, set_dram_channel_width (channel_width=64) (gdb) c Continuing. Breakpoint 2, set_dram_transaction_granularity (cacheline_size=64) (gdb) c Continuing. Breakpoint 1, set_dram_channel_width (channel_width=8) (gdb) c Continuing.

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• C pointers and addresses

  - by yCalleecharan

  Hi, I always thought that *&p = p = &*p in C. I tried this code: #include <stdio.h> #include <stdlib.h> char a[] = "programming"; char *ap = &a[4]; int main(void) { printf("%x %x %x\n", ap, &*(ap), *&(ap)); /* line 13 */ printf("%x %x %x\n\n", ap+1, &*(ap+1), *&(ap+1)); /* line 14 */ } The first printf line (line 13) gives me the addresses: 40b0a8 40b0a8 40b0a8 which are the same as expected. But when I added the second printf line, Borland complains: "first.c": E2027 Must take address of a memory location in function main at line 14 I was expecting to get: 40b0a9 40b0a9 40b0a9. It seems that the expression *&(ap+1) on line 14 is the culprit here. I thought all three pointer expressions on line 14 are equivalent. Why am I thinking wrong? A second related question: The line char *ap = a; points to the first element of array a. I used char *ap = &a[4]; to point to the 5th element of array a. Is the expression char *ap = a; same as the expression char *ap = &a[0]; Is the last expression only more verbose than the previous one? Thanks a lot...

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• How to convert struct to char array in C

  - by falcojr

  I'm trying to convert a struct to a char array to send over the network. However, I get some weird output from the char array when I do. #include <stdio.h> struct x { int x; } __attribute__((packed)); int main() { struct x a; a.x=127; char *b = (char *)&a; int i; for (i=0; i<4; i++) printf("%02x ", b[i]); printf("\n"); for (i=0; i<4; i++) printf("%d ", b[i]); printf("\n"); return 0; } Here is the output for various values of a.x (on an X86 using gcc): 127: 7f 00 00 00 127 0 0 0 128: ffffff80 00 00 00 -128 0 0 0 255: ffffffff 00 00 00 -1 0 0 0 256: 00 01 00 00 0 1 0 0 I understand the values for 127 and 256, but why do the numbers change when going to 128? Why wouldn't it just be: 80 00 00 00 128 0 0 0 Am I forgetting to do something in the conversion process or am I forgetting something about integer representation? *Note: This is just a small test program. In a real program I have more in the struct, better variable names, and I convert to little-endian. *Edit: formatting

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• Using pipes in Linux with C

  - by Dave

  Hi, I'm doing a course in Operating Systems and we're supposed to learn how to use pipes to transfer data between processes. We were given this simple piece of code which demonstrates how to use pipes,but I'm having difficulty understanding it. #include <stdio.h> #include <stdlib.h> #include <unistd.h> main() { int pipefd [2], n; char buff[100] ; if( pipe( pipefd) < 0) { printf("can not create pipe \n"); } printf("read fd = %d, write fd = %d \n", pipefd[0], pipefd[1]); if ( write (pipefd[1],"hello world\n", 12)!= 12) { printf("pipe write error \n"); } if( ( n = read ( pipefd[0] , buff, sizeof ( buff) ) ) <= 0 ) { printf("pipe read error \n"); } write ( 1, buff, n ) ; exit (0); } What does the write function do? It seems to send data to the pipe and also print it to the screen (at least it seems like the second time the write function is called it does this). Does anyone have any suggestions of good websites for learning about topics such as this, FIFO, signals, other basic linux commands used in C?

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• warning: assignment makes pointer from integer without a cast

  - by FILIaS

  Im new in programming c with arrays and files. Im just trying to run the following code but i get warnings like that: warning: assignment makes pointer from integer without a cast Any help? It might be silly... but I cant find what's wrong. FILE *fp; FILE *cw; char filename_game[40],filename_words[40]; int main() { while(1) { /* Input filenames. */ printf("\n Enter the name of the file with the cryptwords array: \n"); gets(filename_game); printf("\n Give the name of the file with crypted words:\n"); gets(filename_words); /* Try to open the file with the game */ if (fp=fopen("crypt.txt","r")!=NULL) { printf("\n Successful opening %s \n",filename_game); fclose(fp); puts("\n Enter x to exit,any other to continue! \n "); if ( (getc(stdin))=='x') break; else continue; } else { fprintf(stderr,"ERROR!%s \n",filename_game); puts("\n Enter x to exit,any other to continue! \n"); if (getc(stdin)=='x') break; else continue; } /* Try to open the file with the names. */ if (cw=fopen("words.txt","r")!=NULL) { printf("\n Successful opening %s \n",filename_words); fclose(cw); puts("\n Enter x to exit,any other to continue \n "); if ( (getc(stdin))=='x') break; else continue; } else { fprintf(stderr,"ERROR!%s \n",filename_words); puts("\n Enter x to exit,any other to continue! \n"); if (getc(stdin)=='x') break; else continue; } } return 0; }

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• Speedup writing C programs using a subset of the Python syntax

  - by psihodelia

  I am constantly trying to optimize my time. Writing a C code takes a lot of time and requires much more keyboard touches than say writing a Python program. However, in order to speed up the time required to create a C program, one can automatize many things. I'd like to write my programs using smth. like Python but with C semantics. It means, all keywords are C keywords, but syntax is optimized. For example, this C code: #include "dsplib.h" #include "coeffs.h" #define MODULENAME "dsplib" #define NUM_SAMPLES 320 typedef float t_Vec; typedef struct s_Inter { char *pc_Name; struct s_Inter *px_Next; }t_Inter; typedef struct s_DspLibControl { t_Vec f_Y; }t_DspLibControl; void v_DspLibName(void) { printf("Module: %s", MODULENAME); printf("\n"); } int v_DspLibInitInterControl(t_DspLibControl *px_Con) { int y; px_Con->f_Y = 0.0; for(int i=0;i<10;i++) { y += i * i; } return y; } in optimized pythonized version can look like: include dsplib, coeffs define MODULENAME="dsplib", NUM_SAMPLES=320 typedef float t_Vec typedef struct s_Inter: char *pc_Name struct s_Inter *px_Next t_Inter typedef struct s_DspLibControl: t_Vec f_Y t_DspLibControl v_DspLibName(): printf("Module: %s", MODULENAME); printf("\n") int v_DspLibInitInterControl(t_DspLibControl *px_Con): int y px_Con->f_Y = 0.0 for int i=0;i<10;i++: y += i * i return y My question is: Do you know any VIM script, which allows to translate an original pythonized C code into a standard C code? For example, one is writing a C code but uses pythonized syntax, once she decides to translate pythonized blocks into standard C, she selects such blocks and press some key. And she doesn't save such pythonized code of course, VIM translates it into standard C.

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• problem with fork()

  - by john

  I'm writing a shell which forks, with the parent reading the input and the child process parsing and executing it with execvp. pseudocode of main method: do{ pid = fork(); print pid; if (p<0) { error; exit; } if (p>0) { wait for child to finish; read input; } else { call function to parse input; exit; } }while condition return; what happens is that i never seem to enter the child process (pid printed is always positive, i never enter the else). however, if i don't call the parse function and just have else exit, i do correctly enter parent and child alternatingly. full code: int main(int argc, char *argv[]){ char input[500]; pid_t p; int firstrun = 1; do{ p = fork(); printf("PID: %d", p); if (p < 0) {printf("Error forking"); exit(-1);} if (p > 0){ wait(NULL); firstrun = 0; printf("\n> "); bzero(input, 500); fflush(stdout); read(0, input, 499); input[strlen(input)-1] = '\0'; } else exit(0); else { if (parse(input) != 0 && firstrun != 1) { printf("Error parsing"); exit(-1); } exit(0); } }while(strcmp(input, "exit") != 0); return 0; }

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• How To Compile YACC And LEX?

  - by nisha

  Actually I'm having YACC file as pos.yacc and LEX file name is pos1.lex.. while compilling I'm getting the folowing error... malathy@malathy:~$ cc lex.yy.c y.tab.c -ly -ll pos1.lex %{ #include "y.tab.h" int yylval; %} DIGIT [0-9]+ %% {DIGIT} {yylval=atoi(yytext);return DIGIT;} [\n ] {} . {return *yytext;} %% yacc file is pos.yacc %token DIGIT %% s:e {printf("%d\n",$1);} e:DIGIT {$$=$1;} |e e "+" {$$=$1+$2;} |e e "*" {$$=$1*$2;} |e e "-" {$$=$1-$2;} |e e "/" {$$=$1/$2;} ; %% main() { yyparse(); } yyerror() { printf("Error"); } so while compiling i m getting like malathy@malathy:~$ cc lex.yy.c y.tab.c -ly -ll pos.y: In function ‘yyerror’: pos.y:16: warning: incompatible implicit declaration of built-in function ‘printf’ pos.y: In function ‘yyparse’: pos.y:4: warning: incompatible implicit declaration of built-in function ‘printf’

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• Syntax error beyond end of program

  - by a_m0d

  I am experimenting with writing a toy compiler in ocaml. Currently, I am trying to implement the offside rule for my lexer. However, I am having some trouble with the ocaml syntax (the compiler errors are extremely un-informative). The code below (33 lines of it) causes an error on line 34, beyond the end of the source code. I am unsure what is causing this error. open Printf let s = (Stack.create():int Stack.t); let rec check x = ( if Stack.is_empty s then Stack.push x s else if Stack.top s < x then ( Stack.push x s; printf "INDENT\n"; ) else if Stack.top s > x then ( printf "DEDENT\n"; Stack.pop s; check x; ) else printf "MATCHED\n"; ); let main () = ( check 0; check 4; check 6; check 8; check 5; ); let _ = Printexc.print main () Ocaml output: File "lexer.ml", line 34, characters 0-0: Error: Syntax error Can someone help me work out what the error is caused by and help me on my way to fixing it?

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• C Programming: malloc() inside another function

  - by vikramtheone

  Hi Guys, I need help with malloc() inside another function. I'm passing a pointer and size to the function from my main() and I would like to allocate memory for that pointer dynamically using malloc() from inside that called function, but what I see is that.... the memory which is getting allocated is for the pointer declared withing my called function and not for the pointer which is inside the main(). How should I pass a pointer to a function and allocate memory for the passed pointer from inside the called function? Can anyone throw light on this? Help!!! Vikram I have written the following code and I get the output as shown below SOURCE: main() { unsigned char *input_image; unsigned int bmp_image_size = 262144; if(alloc_pixels(input_image, bmp_image_size)==NULL) printf("\nPoint2: Memory allocated: %d bytes",_msize(input_image)); else printf("\nPoint3: Memory not allocated"); } signed char alloc_pixels(unsigned char *ptr, unsigned int size) { signed char status = NO_ERROR; ptr = NULL; ptr = (unsigned char*)malloc(size); if(ptr== NULL) { status = ERROR; free(ptr); printf("\nERROR: Memory allocation did not complete successfully!"); } printf("\nPoint1: Memory allocated: %d bytes",_msize(ptr)); return status; } PROGRAM OUTPUT: Point1: Memory allocated ptr: 262144 bytes Point2: Memory allocated input_image: 0 bytes

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• JNI Stream binary data from C++ to Java

  - by Cliff

  I need help passing binary data into Java. I'm trying to use jbytearray but when the data gets into Java it appears corrupt. Can somebody give me a hand? Here's a snip of some example code. First the native C++ side: printf("Building audio array copy\n"); jbyteArray rawAudioCopy = env-NewByteArray(10); jbyte toCopy[10]; printf("Filling audio array copy\n"); char theBytes[10] = {0,1,2,3,4,5,6,7,8,9}; for (int i = 0; i < sizeof(theBytes); i++) { toCopy[i] = theBytes[i]; } env->SetByteArrayRegion(rawAudioCopy,0,10,toCopy); printf("Finding object callback\n"); jmethodID aMethodId = env->GetMethodID(env->GetObjectClass(obj),"handleAudio","([B)V"); if(0==aMethodId) throw MyRuntimeException("Method not found error",99); printf("Invoking the callback\n"); env->CallVoidMethod(obj,aMethodId, &rawAudioCopy); and then the Java callback method: public void handleAudio(byte[] audio){ System.out.println("Audio supplied to Java [" + audio.length + "] bytes"); byte[] expectedAudio = {0,1,2,3,4,5,6,7,8,9}; for (int i = 0; i < audio.length; i++) { if(audio[i]!= expectedAudio[i]) System.err.println("Expected byte " + expectedAudio[i] + " at byte " + i + " but got byte " + audio[i]); else System.out.print('.'); } System.out.println("Audio passed back accordingly!"); } I get the following output when the callback is invoked: library loaded! Audio supplied to Java [-2019659176] bytes Audio passed back accordingly!

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• Passing pointer into function, data appears initialized in function, on return appears uninitialize

  - by Luke Mcneice

  Im passing function GetCurrentDate() the pointer to a tm struct. Within that function I printf the uninitialized data, then the initialized. Expected results. However when i return the tm struct appears uninitialized. See console output bellow. What am i doing wrong? uninitialized date:??? ???-1073908332 01:9448278:-1073908376 -1217355836 initialized date:Wed May 5 23:08:40 2010 Caller date:??? ???-1073908332 01:9448278:-1073908376 -121735583 int main() { test(); } int test() { struct tm* CurrentDate; GetCurrentDate(CurrentDate); printf("Caller date:%s\n",asctime (CurrentDate)); return 1; } int GetCurrentDate(struct tm* p_ReturnDate) { printf("uninitialized date:%s\n",asctime (p_ReturnDate)); time_t m_TimeEntity; m_TimeEntity = time(NULL); //setting current time into a time_t struct p_ReturnDate = localtime(&m_TimeEntity); //converting time_t to tm struct printf("initialized date:%s\n",asctime (p_ReturnDate)); return 1; }

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• I am trying to find how many vowels and consonants in my string in C

  - by John Walter

  #include <stdio.h> #include <string.h> int main() { int i; int counter=0, counter2=0; char *s; char name[30]; char vowel[6] = "AEIOU"; char consonants[21] = "BCDFGHJKLMNPQRSTVWXYZ"; printf ("input the string: "); scanf ("%s", name); printf ("The string is %s\n", name); for (i=0; name[i]!='\0'; i++) { if (s = strchr(vowel, name[i])) { counter++; } else if (s =strchr(consonants, name[i])) { counter2++; } printf ("First counter is %d\n", counter); printf ("The second counter is %d\n", counter2); return 0; } } And the question is, what is wrong with my code? why counter is not working? Because I tried a lot of ways, and nothing works, maybe someone can explain for me.

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• C: Global ,Static variables understanding

  - by pavun_cool

  Hi All, In following program . I have one doubt. I have declared one global variable . I am printing the address of the global variable in the function . It is giving me same address when I am not changing the value of global . If I did any changes in the global variables It is giving me different address why...........? Like that it is happening for static also. #include<stdio.h> int global=10 ; // Global variables void function(); main() { global=20; printf ( " %p \n" , global ) ; printf ( " Val: %d\n", global ) ; function(); new(); } void function() { global=30; printf ( " %p \n" , global ) ; printf ( " Val: %d\n", global ) ; } Thanks.

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• Garbage data from serial port.

  - by sasayins

  Hi I wrote a code in Linux platform that read the data in serial port, my code below: int fd; char *rbuff=NULL; struct termios new_opt, old_opt; int ret; fd = open("/dev/ttyS0", O_RDWR | O_NOCTTY); if( fd == -1 ) { printf("Can't open file: %s\n", strerror(errno)); return -1; } tcgetattr(fd, &old_opt); new_opt.c_cflag = B115200 | CS8 | CLOCAL | CREAD; new_opt.c_iflag = IGNPAR /*| ICRNL*/; new_opt.c_oflag = 0; new_opt.c_lflag = ICANON; tcsetattr(fd, TCSANOW, &new_opt); rbuff = malloc(NBUFF); printf("reading..\n"); memset(rbuff,0x00,NBUFF); ret = read(fd, rbuff, NBUFF); printf("value:%s",rbuff); if(ret == -1) { printf("Read error:%s\n",strerror(errno)); return -1; } tcsetattr(fd, TCSANOW, &old_opt); close(fd); My problem is the code above doesn't read the first data that was transmitted, then the second transmission the data is garbage, then the third is the normal data. Did I missed a setting in the serial port? Thanks.

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• Generating Fibonacci Numbers Using variable-Length Arrays Code Compiler Error.

  - by Nano HE

  Compile error in vs2010(Win32 Console Application Template) for the code below. How can I fix it. unsigned long long int Fibonacci[numFibs]; // error occurred here error C2057: expected constant expression error C2466: cannot allocate an array of constant size 0 error C2133: 'Fibonacci' : unknown size Complete code attached(It's a sample code from programming In c -3E book. No any modify) int main() { int i, numFibs; printf("How may Fibonacci numbers do you want (between 1 to 75)? "); scanf("%i", &numFibs); if ( numFibs < 1 || numFibs > 75){ printf("Bad number, sorry!\n"); return 1; } unsigned long long int Fibonacci[numFibs]; Fibonacci[0] = 0; // by definition Fibonacci[1] = 1; // ditto for ( i = 2; i < numFibs; ++i) Fibonacci[i] = Fibonacci[i-2] + Fibonacci[i-1]; for ( i = 0; i < numFibs; ++i) printf("%11u",Fibonacci[i]); printf("\n"); return 0; }

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• Segmentation Fault

  - by Biranchi

  Hi All, I have the following piece of code for getting the hostname and IP address, #include <stdlib.h> #include <stdio.h> #include <netdb.h> /* This is the header file needed for gethostbyname() */ #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> int main(int argc, char *argv[]) { struct hostent *he; if (argc!=2){ printf("Usage: %s <hostname>\n",argv[0]); exit(-1); } if ((he=gethostbyname(argv[1]))==NULL){ printf("gethostbyname() error\n"); exit(-1); } printf("Hostname : %s\n",he->h_name); /* prints the hostname */ printf("IP Address: %s\n",inet_ntoa(*((struct in_addr *)he->h_addr))); /* prints IP address */ } but i am getting a warning and segmentation fault as host.c: In function ‘main’: host.c:24: warning: format ‘%s’ expects type ‘char *’, but argument 2 has type ‘int’ What is the error in the code ?? Thanks

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• C program - Seg fault, cause of

  - by resonant_fractal

  Running this gives me a seg fault (gcc filename.c -lm), when i enter 6 (int) as a value. Please help me get my head around this. The intended functionality has not yet been implemented, but I need to know why I'm headed into seg faults already. Thanks! #include<stdio.h> #include<math.h> int main (void) { int l = 5; int n, i, tmp, index; char * s[] = {"Sheldon", "Leonard", "Penny", "Raj", "Howard"}; scanf("%d", &n); //Solve Sigma(Ai*2^(i-1)) = (n - k)/l if (n/l <= 1) printf("%s\n", s[n-1]); else { tmp = n; for (i = 1;;) { tmp = tmp - (l * pow(2,i-1)); if (tmp <= 5) { // printf("Breaking\n"); break; } ++i; } printf("Last index = %d\n", i); // ***NOTE*** //Value lies in next array, therefore ++i; index = tmp + pow(2, n-1); printf("%d\n", index); } return 0; }

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• How to access variables in shared memory

  - by user1723361

  I am trying to create a shared memory segment containing three integers and an array. The segment is created and a pointer is attached, but when I try to access the values of the variables (whether changing, printing, etc.) I get a segmentation fault. Here is the code I tried: #include <stdio.h> #include <stdbool.h> #include <stdlib.h> #include <errno.h> #include <sys/types.h> #include <sys/ipc.h> #include <sys/sem.h> #define SIZE 10 int* shm_front; int* shm_end; int* shm_count; int* shm_array; int shm_size = 3*sizeof(int) + sizeof(shm_array[SIZE]); int main(int argc, char* argsv[]) { int shmid; //create shared memory segment if((shmid = shmget(IPC_PRIVATE, shm_size, 0644)) == -1) { printf("error in shmget"); exit(1); } //obtain the pointer to the segment if((shm_front = (int*)shmat(shmid, (void *)0, 0)) == (void *)-1) { printf("error in shmat"); exit(1); } //move down the segment to set the other pointers shm_end = shm_front + 1; shm_count = shm_front + 2; shm_array = shm_front + 3; //tests on shm //*shm_end = 10; //gives segmentation fault //printf("\n%d", *shm_front); //gives segmentation fault //clean-up //get rid of shared memory shmdt(shm_front); shmctl(shmid, IPC_RMID, NULL); //printf("\n\n"); return 0; } I tried accessing the shared memory by dereferencing the pointer to the struct, but got a segmentation fault each time.

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• Pointer and malloc issue

  - by Andy

  I am fairly new to C and am getting stuck with arrays and pointers when they refer to strings. I can ask for input of 2 numbers (ints) and then return the one I want (first number or second number) without any issues. But when I request names and try to return them, the program crashes after I enter the first name and not sure why. In theory I am looking to reserve memory for the first name, and then expand it to include a second name. Can anyone explain why this breaks? Thanks! #include <stdio.h> #include <stdlib.h> void main () { int NumItems = 0; NumItems += 1; char* NameList = malloc(sizeof(char[10])*NumItems); printf("Please enter name #1: \n"); scanf("%9s", NameList[0]); fpurge(stdin); NumItems += 1; NameList = realloc(NameList,sizeof(char[10])*NumItems); printf("Please enter name #2: \n"); scanf("%9s", NameList[1]); fpurge(stdin); printf("The first name is: %s",NameList[0]); printf("The second name is: %s",NameList[1]); return 0; }

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• Print the first line of a file C programming

  - by Pedro

  void cabclh(){ FILE *fp; char *val, aux; int i=0; char *result, cabeca[60]; fp=fopen("trabalho.txt","r"); if(fp==NULL){ printf("ERROR\n"); return ; } val=(char*)calloc(aux, sizeof(char)); while(fp='\n'){ fgets(cabeca,60,fp); printf("%s\n",cabeca); } fclose(fp); free(fp); } I want to open a file and print the first line. the problem here is in while(fp='\n'), what i'm doing wrong. How can i make a function that recognize the first char from a file... like: FILE *arq; char info[20]; arq=fopen("trabalho.txt","r"); if(fp==NULL){ printf("ERROR\n"); return ; } if(fp[0]='-'){ //check if the first element is a '-' printf("It's info\n"); }

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• Why does mmap() fail with ENOMEM on a 1TB sparse file?

  - by metadaddy

  I've been working with large sparse files on openSUSE 11.2 x86_64. When I try to mmap() a 1TB sparse file, it fails with ENOMEM. I would have thought that the 64 bit address space would be adequate to map in a terabyte, but it seems not. Experimenting further, a 1GB file works fine, but a 2GB file (and anything bigger) fails. I'm guessing there might be a setting somewhere to tweak, but an extensive search turns up nothing. Here's some sample code that shows the problem - any clues? #include <errno.h> #include <fcntl.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/mman.h> #include <sys/types.h> #include <unistd.h> int main(int argc, char *argv[]) { char * filename = argv[1]; int fd; off_t size = 1UL << 40; // 30 == 1GB, 40 == 1TB fd = open(filename, O_RDWR | O_CREAT | O_TRUNC, 0666); ftruncate(fd, size); printf("Created %ld byte sparse file\n", size); char * buffer = (char *)mmap(NULL, (size_t)size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); if ( buffer == MAP_FAILED ) { perror("mmap"); exit(1); } printf("Done mmap - returned 0x0%lx\n", (unsigned long)buffer); strcpy( buffer, "cafebabe" ); printf("Wrote to start\n"); strcpy( buffer + (size - 9), "deadbeef" ); printf("Wrote to end\n"); if ( munmap(buffer, (size_t)size) < 0 ) { perror("munmap"); exit(1); } close(fd); return 0; }

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• Functions and arrays

  - by Ordo

  Hello! My little program below shall take 5 numbers from the user, store them into an array of integers and use a function to print them out. Sincerly it doesn't work and nothing is printed out. I can't find a mistake, so i would be glad about any advice. Thanks. #include <stdio.h> void printarray(int intarray[], int n) { int i; for(i = 0; i < n; i ++) { printf("%d", intarray[i]); } } int main () { const int n = 5; int temp = 0; int i; int intarray [n]; char check; printf("Please type in your numbers!\n"); for(i = 0; i < n; i ++) { printf(""); scanf("%d", &temp); intarray[i] = temp; } printf("Do you want to print them out? (yes/no): "); scanf("%c", &check); if (check == 'y') printarray(intarray, n); getchar(); getchar(); getchar(); getchar(); return 0; }

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