How to I give the user the ability to name the output .txt file? Here is all I have right now.
FILE *f = fopen("output.txt", "a");
CallXXXMethod undefined using JNI in C
There are few fixes required in the code: CallIntMethod should be (*env)->CallIntMethod class Test should be public Invocation should be jint age = (*env)->CallIntMethod(env, mod_obj, mid, NULL); Note that you need class name to call a static function but an object to call a method. (cls2 -> person) mid =...
Strings vs binary for storing variables inside the file format
Speaking as someone who's had to do exactly what you're talking about a number of time, rr got it basically right, but I would change the emphasis a little. For file versioning, text is basically the winner. Since you're using an hdf5 library, I assume both serializing and parsing are...
Array breaking in Pebble C
c,arrays,pebble-watch,cloudpebble
The problem is this line static char *die_label = "D"; That points die_label to a region of memory that a) should not be written to, and b) only has space for two characters, the D and the \0 terminator. So the strcat is writing into memory that it shouldn't be....
How to get rid of .ignore file in Git?
.gitignore is just like any other file under version control, so yes, you can delete it. However, keep in mind that it probably has entries in it that should be kept, so instead of deleting it, I would just modify it so that your jar files are no longer ignored.
C binary tree sort - extending it
c,binary-tree,binary-search-tree
a sample to modify like as void inorder ( struct btreenode *, int ** ) ; int* sort(int *array, int arr_size) { struct btreenode *bt = NULL; int i, *p = array; for ( i = 0 ; i < arr_size ; i++ ) insert ( &bt, array[i] ) ;...
C programming - Confusion regarding curly braces
The only difference between the two is the scope of the else. Without the braces, it spans until the end of the full statement, which is the next ;, i.e the next line: else putchar(ch); /* end of else */ lastch = ch; /* outside of if-else */ With the...
Does strlen() always correctly report the number of char's in a pointer initialized string?
What strlen does is basically count all bytes until it hits a zero-byte, the so-called null-terminator, character '\0'. So as long as the string contains a terminator within the bounds of the memory allocated for the string, strlen will correctly return the number of char in the string. Note that...
execl() works on one of my code, but doesn't work on another
My C is a bit rusty but your code made many rookie mistakes. execl will replace the current process if it succeeds. So the last line ("i have no idea why") won't print if the child can launch successfully. Which means... execl failed and you didn't check for it! Hint:...
scanf get multiple values at once
c,char,segmentation-fault,user-input,scanf
I'm not saying that it cannot be done using scanf(), but IMHO, that's not the best way to do it. Instead, use fgets() to read the whole like, use strtok() to tokenize the input and then, based on the first token value, iterate over the input string as required. A...
C language, vector of struct, miss something?
What is happening is that tPeca pecaJogo[tam]; is a local variable, and as such the whole array is allocated in the stack frame of the function, which means that it will be deallocated along with the stack frame where the function it self is loaded. The reason it's working is...
Galois LFSR - how to specify the output bit number
If you need bit k (k = 0 ..15), you can do the following: return (lfsr >> k) & 1; This shifts the register kbit positions to the right and masks the least significant bit....
Reverse ^ operator for decryption
c,algorithm,security,math,encryption
This is not a power operator. It is the XOR operator. The thing that you notice for the XOR operator is that x ^ k ^ k == x. That means that your encryption function is already the decryption function when called with the same key and the ciphertext instead...
How does ((a++,b)) work? [duplicate]
In your first code, Case 1: return reverse(i++); will cause stack overflow as the value of unchanged i will be used as the function argument (as the effect of post increment will be sequenced after the function call), and then i will be increased. So, it is basically calling the...
Loop through database table and compare user input
If you are only looking for fields that match the input, you'll want to search the database using the input string. In other words, write your query string so that it only gives you results that match the user input. This will be much faster than searching through every returned...
Efficient comparison of small integer vectors
c,integer,compare,bit-manipulation,string-comparison
It's possible to do this using bit-manipulation. Space your values out so that each takes up 5 bits, with 4 bits for the value and an empty 0 in the most significant position as a kind of spacing bit. Placing a spacing bit between each value stops borrows/carries from propagating...
How to control C Macro Precedence
You can redirect the JOIN operation to another macro, which then does the actual pasting, in order to enforce expansion of its arguments: #define VAL1CHK 20 #define NUM 1 #define JOIN1(A, B, C) A##B##C #define JOIN(A, B, C) JOIN1(A, B, C) int x = JOIN(VAL,NUM,CHK); This technique is often used...
CGO converting Xlib XEvent struct to byte array?
As mentioned in the cgo documentation: As Go doesn't have support for C's union type in the general case, C's union types are represented as a Go byte array with the same length. Another SO question: Golang CGo: converting union field to Go type or a go-nuts mailing list post...
Text justification C language
From printf's manual: The field width An optional decimal digit string (with nonzero first digit) specifying a minimum field width. If the converted value has fewer characters than the field width, it will be padded with spaces on the left (or right, if the left-adjustment flag has been given). Instead...
How to increment the value of an unsigned char * (C)
I am assuming your pointer refers to 20 bytes, for the 160 bit value. (An alternative may be text characters representing hex values for the same 160 bit meaning, but occupying more characters) You can declare a class for the data, and implement a method to increment the low order...
free causing different results from malloc
Every time you are creating your string, you are not appending a null terminator, which causes the error. So change this: for(j=0; j<rem_len; j++) { if(j != i) { remaining_for_next[index_4_next] = remaining[j]; index_4_next++; } } to this: for(j=0; j<rem_len; j++) { if(j != i) { remaining_for_next[index_4_next] = remaining[j]; index_4_next++; }...
Is it safe to read and write on an array of 32 bit data byte by byte?
Yes, this is correct. The only danger would be generating a bit pattern that does not correspond to any int, but on modern systems there are no such patterns. Also, if the data type was uint32_t specifically, those are prohibited from having any such patterns anyway. Note that the inverse...
Does realloc() invalidate all pointers?
c,pointers,dynamic-memory-allocation,behavior,realloc
Yes, ptr2 is unaffected by realloc(), it has no connection to realloc() call whatsoever(as per the current code). However, FWIW, as per the man page of realloc(), (emphasis mine) The realloc() function returns a pointer to the newly allocated memory, which is suitably aligned for any kind of variable and...
How to read string until two consecutive spaces?
The scanf family of functions are good for simple parsing, but not for more complicated things like you seem to do. You could probably solve it by using e.g. strstr to find the comment starter "//", terminate the string there, and then remove trailing space....
fread(), solaris to unix portability and use of uninitialised values
c,linux,memory,stack,portability
Q 1. why is ch empty even after fread() assignment? (Most probably) because fread() failed. See the detailed answer below. Q 2.Is this a portability issue between Solaris and Linux? No, there is a possible issue with your code itself, which is correctly reported by valgrind. I cannot quite...
Delphi - Use a string variable's name in assignfile()
Is it possible to use a variable in the AssignFile command? Yes. The second parameter of AssignFile has type string. The expression cFileDir + '\' + sFile has type string. FWIW, AssignFile is known as a function rather than a command. Getting on top of terminology like this will...
Storing columns on disk and reading rows
Mentioned solution with fseek is good. However, it can be very slow for large matrices (as disks don't like random access, especially very far away). To speed up things, you should use blocking. I'll show a basic concept, and can explain it further if you need. First, you split your...
Is there Predefined-Macros define about byte order in armcc
Well according to this page: http://www.keil.com/support/man/docs/armccref/armccref_BABJFEFG.htm You have __BIG_ENDIAN which is defined when compiling for a big endian target....
How does this code print odd and even?
In binary any numbers LSB (Least Significant Bit) is set or 1 means the number is odd, and LSB 0 means the number is even. Lets take a look: Decimal binary 1 001 (odd) 2 010 (even) 3 011 (odd) 4 100 (even) 5 101 (odd) SO, the following line...
Saying there are 0 arguments when I have 2? Trying to open a CSV file to write into
I believe the problem is with Dir.foreach, not CSV.open. You need to supply a directory to foreach as an argument. That's why you are getting the missing argument error. Try: Dir.foreach('/path/to_my/directory') do |current_file| I think the open that is referenced in the error message is when Dir is trying to...
Rust: Lifetime of String from file [duplicate]
The string bound to "s" will be deallocated once the function ends ("s" goes out of scope), so you cannot return a reference to its contents outside the function. The best way is to return the string itself: fn read_shader_code(string_path: &str) -> String { let path = Path::new(string_path); let display...
Disadvantages of calling realloc in a loop
c,memory-management,out-of-memory,realloc
When you allocate/deallocate memory many times, it may create fragmentation in the memory and you may not get big contiguous chunk of the memory. When you do a realloc, some extra memory may be needed for a short period of time to move the data. If your algorithm does...
How convert unsigned int to unsigned char array
#include <stdio.h> int main() { unsigned int i = 0x557e89f3; unsigned char c[4]; c[0] = i & 0xFF; c[1] = (i>>8) & 0xFF; c[2] = (i>>16) & 0xFF; c[3] = (i>>24) & 0xFF; printf("c[0] = %x \n", c[0]); printf("c[1] = %x \n", c[1]); printf("c[2] = %x \n", c[2]); printf("c[3] =...
How can I align stack to the end of SRAM?
c,embedded,stm32,gnu-arm,coocox
I've found the reason: that's because stack size is actually fixed and it is located in heap (if I could call it heap). In file startup_stm32f10x*.c there is a section: /*----------Stack Configuration----------*/ #define STACK_SIZE 0x00000100 /*!< The Stack size suggest using even number */ And at then very next line:...
Segmentation fault with generating an RSA and saving in ASN.1/DER?
pub_l = malloc(sizeof(pub_l)); is simply not needed. Nor is priv_l = malloc(sizeof(priv_l));. Remove them both from your function. You should be populating your out-parameters; instead you're throwing out the caller's provided addresses to populate and (a) populating your own, then (b) leaking the memory you just allocated. The result is...
Passing int using char pointer in C
Programs simply do not take integers as arguments, they take strings. Those strings can be decimal representations of integers, but they are still strings. So you are asking how to do something that simply doesn't make any sense. Twenty is an integer. It's the number of things you have if...
Segmentation Fault if I don't say int i=0
c,arrays,segmentation-fault,initialization,int
In your code, int i is an automatic local variable. If not initialized explicitly, the value held by that variable in indeterministic. So, without explicit initialization, using (reading the value of ) i in any form, like array[i] invokes undefined behaviour, the side-effect being a segmentation fault. Isn't it automatically...
ValueError: dictionary update sequence element #0 has length 1; 2 is required while reading from file
dict() does not parse Python dictionary literal syntax; it won't take a string and interpret its contents. It can only take another dictionary or a sequence of key-value pairs, your line doesn't match those criteria. You'll need to use the ast.literal_eval() function instead here: from ast import literal_eval if line.startswith(self.kind):...
IllegalStateException: Iterator already obtained [duplicate]
You have to call DirectoryStream<Path> files = Files.newDirectoryStream(dir); each time you iterate over the files. Pls check this question... java.lang.IllegalStateException: Iterator already obtained...
What does `strcpy(x+1, SEQX)` do?
The pointer + offset notation is used as a convenient means to reference memory locations. In your case, the pointer is provided by malloc() after allocating sufficient heap memory, and represents an array of M + 2 elements of type char, thus the notation as used in your code represents...
Infinite loop with fread
If you're "trying to allocate an array 64 bytes in size", you may consider uint8_t Buffer[64]; instead of uint8_t *Buffer[64]; (the latter is an array of 64 pointers to byte) After doing this, you will have no need in malloc as your structure with a 64 bytes array inside is...
OpenGL glTexImage2D memory issue
Which man page are you quoting? There are multiple man pages available, not all mapping to the same OpenGL version. Anyways, the idea behind the + 2 (border) is to have 2 multiplied by the value of border, which is in your case 0. So your code is just fine....
Counting bytes received by posix read()
Yes, temp_uart_count will contain the actual number of bytes read, and obviously that number will be smaller or equal to the number of elements of temp_uart_data. If you get 0, it means that the end of file (or an equivalent condition) has been reached and there is nothing else to...
Set precision dynamically using sprintf
Yes, you can do that. You need to use an asterisk * as the field width and .* as the precision. Then, you need to supply the arguments carrying the values. Something like sprintf(myNumber,"%*.*lf",A,B,a); Note: A and B need to be type int. From the C11 standard, chapter ยง7.21.6.1, fprintf()...
What all local variables goto Data/BSS segment?
"local" in this context means file scope. That is: static int local_data = 1; /* initialised local data */ static int local_bss; /* uninitialised local bss */ int global_data = 1; /* initialised global data */ int global_bss; /* uninitialised global bss */ void main (void) { // Some code...
Is post-increment operator guaranteed to run instantly?
This code is broken for two reasons: Accessing a variable twice between sequence points, for other purposes than to determine which value to store, is undefined behavior. There are no sequence points between the evaluation of function parameters. Meaning anything could happen, your program might crash & burn (or more...
getchar() not working in c
c,while-loop,char,scanf,getchar
That's because scanf() left the trailing newline in input. I suggest replacing this: ch = getchar(); With: scanf(" %c", &ch); Note the leading space in the format string. It is needed to force scanf() to ignore every whitespace character until a non-whitespace is read. This is generally more robust than...
VS2012 Identifer not found when part of static lib
c,visual-studio-2012,linker,static-libraries
C++ uses something called name mangling when it creates symbol names. It's needed because the symbol names must contain the complete function signature. When you use extern "C" the names will not be mangled, and can be used from other programming languages, like C. You clearly make the shunt library...
C++ / C #define macro calculation
Are DETUNE1 and DETUNE2 calculated every time it is called? Very unlikely. Because you are calling sqrt with constants, most compilers would optimize the call to the sqrt functions and replace it with a constant value. GCC does that at -O1. So does clang. (See live). In the general...
Changing file name to the user's name PHP
You need to change your $target_file variable to the name you want, since this is what gets passed into move_uploaded_file(). I don't see anywhere in your code where you actually set this variable to their username (right now it's still using the name they selected when they uploaded it). Without...
Program to reverse a string in C without declaring a char[]
Important: scanf(" %s", name); has no bounds checking on the input. If someone enters more than 255 characters into your program, it may give undefined behaviour. Now, you have the char array you have the count (number of char in the array), why do you need to bother doing stuffs...