calloc

Our code involves a POD (Plain Old Datastructure) struct (it is a basic c++ struct that has other structs and POD variables in it that needs to get initialized in the beginning.) Based one what I've read , it seems that: myStruct = (MyStruct*)calloc(1, sizeof(MyStruct)); should initialize all the values to zero, as does: myStruct = new MyStruct(); However, when the struct is initialized in the second way, Valgrind later complains "conditional jump or move depends on uninitialised value(s)" when those variables are used. Is my understanding flawed here, or is Valgrind throwing false positives?

1 ，关于 malloc() 函数 函数调用的一般形式： （类型标识符 * ） malloc(size) malloc() 函数的功能是在内存动态分配一个长度为 size 的一个连续空间，含数返回值是该区域的首地址。 （类型标识符 * ）是强制类型转换。因为函数返回的指针的是五类型的，用户根据存储空间的用途把函数调用返回的指针强制转换为相应的类型。 size 是一个无符号数，单位是字节。 2 ， calloc() 函数 函数调用的一般格式： （类标识符 * ） calloc(n,size) calloc() 函数的功能是在内存动态分配 n 个长度为 size 的连续空间，函数返回值是该区域的首地址。 为正整数。 3 ， free() 函数 函数调用一般形式： Free( 指针变量名 ); 代码 #include " iostream " using namespace std; float average( int * p, int n) { int i; float ave = 0 ; for (i = 0 ;i < n;i ++ ) ave +=* (p + i); return ave / n; 10 11 } int main() { int i,n, * p; cin >> n; p = ( int * )malloc(n * sizeof ( int )); // 或p

IMO one is enough, why does calloc require to split it into two arguments? I'd guess that this is probably history and predates the times where C had prototypes for functions. At these times without a prototype the arguments basically had to be int , the typedef size_t probably wasn't even yet invented. But then INTMAX is the largest chunk you could allocate with malloc and splitting it up in two just gives you more flexibility and allows you to allocate really large arrays. Even at that times there were methods to obtain large pages from the system that where zeroed out by default, so

I have a struct where I put all the information about the players. That's my struct: struct player{ int startingCapital; int currentCapital; int startingPosition; int currentPosition; int activePlayer; int canPlay; }; And that's my main: #include <stdio.h> #include <stdlib.h> #include "header.h" int main(int argc, char *argv[]) { int s,i,numOfPlayers; struct player *players; printf("Give the number of players: \n"); scanf("%d",&numOfPlayers); players = (struct player *)calloc(numOfPlayers,sizeof(struct player)); system("PAUSE"); return 0; } I'm asking the user to give the number of players and

From man realloc:The realloc() function returns a pointer to the newly allocated memory, which is suitably aligned for any kind of variable and may be different from ptr, or NULL if the request fails. So in this code snippet: ptr = (int *) malloc(sizeof(int)); ptr1 = (int *) realloc(ptr, count * sizeof(int)); if(ptr1 == NULL){ //reallocated pointer ptr1 printf("Exiting!!\n"); free(ptr); exit(0); }else{ free(ptr); //to deallocate the previous memory block pointed by ptr so as not to leave orphaned blocks of memory when ptr=ptr1 executes and ptr moves on to another block ptr = ptr1; /