- What is Pre-Increment. If the increment operator is placed before the operator variable like c then it is called pre-increment. In this, +1 is added to the value of the first operator ie variable.
- Increment and decrement operators are unary operators that add or subtract one, to or from their operand, respectively.They are commonly implemented in imperative programming languages. C-like languages feature two versions (pre- and post-) of each operator with slightly different semantics. In languages syntactically derived from B (including C and its various derivatives), the increment.
Tag: c,pointers,compilation,compiler-errors,dereference
To my function i get a void pointer, I would like to point to the next location considering the incoming pointer is of char type.
The increment operator adds 1 to its operand, and the decrement operator - subtracts 1 from its operand. Thus − x = x+1; is the same as x; And similarly − x = x-1; is the same as x-; Both the increment and decrement operators can either precede (prefix) or follow (postfix) the operand. Increment and decrement operators in c are explained with examples. Increment operator in c is represented by and decrement operator in c is represented b. Increment and Decrement Operator in C. Increment Operators are used to increased the value of the variable by one and Decrement Operators are used to decrease the value of the variable by one in C programs. Both increment and decrement operator are used on a single operand or variable, so it is called as a unary operator.
I get the following compilation error:
Is this an issue with the priority of operators?
A cast does not yield an lvalue (see section 6.5.4 footnote 104 of C11 standard), therefore you can't apply post increment ++ operator to its result.
c-faq: 4.5:
In C, a cast operator does not mean 'pretend these bits have a different type, and treat them accordingly'; it is a conversion operator, and by definition it yields an rvalue, which cannot be assigned to, or incremented with ++. (It is either an accident or a deliberate but nonstandard extension if a particular compiler accepts expressions such as the above.)
Try this instead
execl() works on one of my code, but doesn't work on another
c,execl
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:...
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...
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...
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] ) ;...
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...
OpenGL glTexImage2D memory issue
c,opengl
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....
How convert unsigned int to unsigned char array
c++,c
#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] =...
Galois LFSR - how to specify the output bit number
c,prng,shift-register
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....
C programming - Confusion regarding curly braces
c,scope
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...
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 control C Macro Precedence
c,macros
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...
How to increment the value of an unsigned char * (C)
c++,c,openssl,byte,sha1
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
c,string,malloc,free
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++; }...
C language, vector of struct, miss something?
c,vector,struct
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...
Does strlen() always correctly report the number of char's in a pointer initialized string?
c,strlen
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...
Is there Predefined-Macros define about byte order in armcc
c,armcc,predefined-macro
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....
What all local variables goto Data/BSS segment?
c++,c,nm
'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...
Passing iterator's element to a function: wrong type of pointer
c++,pointers,stl,iterator
Preferred option: change isPrime to take a long (and pass *it to it). Secondary option: pass &*it instead of it. Your original code doesn't work because it is an iterator (which is a class) whereas the function expected long int * and there is no implicit conversion from iterator to...
Counting bytes received by posix read()
c,function,serial-port,posix
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...
Call template function for the value of a pointer out of a template function, in C++
c++,templates,pointers,c++11
The whole body of your template function needs to compile for the types it's instantiated with, regardless of whether or not a branch will ever be taken. To get around this issue, you can define separate functions for when T is a pointer and when it's not. Using SFINAE: template...
Passing int using char pointer in C
c,exec,ipc
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...
memory content not erased after deleting my pointer (on a simple example) [duplicate]
c++,pointers,memory-management
It may or may not print the same value after delete operation. So simply what you are observing is an undefined behavior.
How does this code print odd and even?
c,if-statement,macros,logic
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...
How does ((a++,b)) work? [duplicate]
c,function,recursion,comma
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...
Can assignment from a const_iterator dereference cause undefined behaviour?
c++,pointers,pass-by-reference,undefined-behavior,const-iterator
The code is perfectly fine. You're not stripping away any constness (there's no way to do that implicitly in C++). *it gives you a const intp &. You're copying the pointer referred to by that reference into arg. Copying from something does not strip constness away. The assignment to arg...
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...
Is post-increment operator guaranteed to run instantly?
c,c89,post-increment,ansi-c
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...
Text justification C language
c,text,alignment
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...
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...
CGO converting Xlib XEvent struct to byte array?
c,go,xlib,cgo
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...
Function pointer to singleton class instance function
c++,oop,pointers,singleton
Simply create a normal class without static methods, ditch the singleton pattern aside, and create an instance. The burden of singleton pattern usually outweigh any benefit....
How to read string until two consecutive spaces?
c,format,sscanf,c-strings
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....
Parameters to use in a referenced function c++
c++,pointers,reference
Your code makes no sense, why are you passing someStruct twice? For the reference part, you should have something like: void names(someStruct &s) { // <<<< Pass struct once as a reference cout << 'First Name: ' << 'n'; cin >> s.firstname; cout << 'Last Name: ' << 'n'; cin...
Set precision dynamically using sprintf
c,printf,format-string
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 §7.21.6.1, fprintf()...
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...
Is it safe to read and write on an array of 32 bit data byte by byte?
c,memory,memory-alignment
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...
What does `strcpy(x+1, SEQX)` do?
c,strcpy
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...
Segmentation fault with generating an RSA and saving in ASN.1/DER?
c,openssl,cryptography,rsa
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...
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:...
Loop through database table and compare user input
mysql,c
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...
C++ / C #define macro calculation
c++,c,macros
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...
double* android ndk crash
c++,pointers,android-ndk
I see several possible causes. First of all, casting char* to double* and then accessing it through that pointer is undefined behavior. Most of time it works, but you are warned. Pointer misalignment. double is most likely supposed to be aligned to 8 bytes, and you read it through pointer...
Post Increment Operator
VS2012 Identifer not found when part of static lib
c,visual-studio-2012,linker,static-libraries
How To Increment In C
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...
Infinite loop with fread
c,arrays,loops,malloc,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...
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...
Program to reverse a string in C without declaring a char[]
c,string,pointers,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...
CallXXXMethod undefined using JNI in C
java,c,jni
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 =...
pointer to pointer dynamic array in C++
c++,arrays,pointers
The valid range of indices of an array with N elements is [0, N-1]. Thus instead of for example this loop for (int i=1; i <= n; i++) ^^^^ ^^^^^^ you have to write for ( int i = 0; i < n; i++ ) As you used operator new...