c - Using Strings and Malloc/Realloc -

-

i'll honest, i'm complete novice @ c. thus, things malloc , realloc alien concepts. think have basics down, can't quite there 100%.

while (int args = scanf("%s", string)) {     if (args < 0) break;     count++;      if (array == null) {         array = (char *) malloc(strlen(string));          if (array == null) {             printf("error allocating memory");             exit(1);         }     } else {         printf("%s %d\n", string, strlen(string));         array = (char *) realloc(array, (sizeof(array) + strlen(string) + 1));          if (array == null) {             printf("error allocating memory");             free(array);             exit(1);         }          printf("%lu\n", sizeof(array));     }      strcpy(&array[count - 1], string); }

it's reading terminal - cat file | ./program , bunch of words of arbitrary length. i'm trying them array (array).

edit: should mentino i'm apparently trying access memory didn't allocated: malloc: *** error object 0x7fe9e04039a0: incorrect checksum freed object - object modified after being freed. *** set breakpoint in malloc_error_break debug segmentation fault: 11

looks don't understand pointers, strings , char*s in c. example, here description.

here main problems:

  1. char* not string type. it's pointer place in memory, string data lies char-by-char , terminates char '\0' (null terminator)
  2. thus, strcpy copies bunch of chars 1 place (string variable) another. in case, copies them array, starting element count-1. so, if read string longer 1 char, lost data. want sum lengths of preceding strings , write starting place.
  3. the remaining problem consequence: don't allocate space null terminator during first iteration (which causes strcpy access non-allocated memory , leads message see after program's termination).

Comments

Post a Comment

Popular posts from this blog

c# - How Configure Devart dotConnect for SQLite Code First? -

-
can configure following sample code ? when run following code, error : no entity framework provider found ado.net provider invariant name 'devart.data.sqlite' setting in machine.config <system.data> <dbproviderfactories> <add name="dotconnect sqlite" invariant="devart.data.sqlite" description="devart dotconnect sqlite" type="devart.data.sqlite.sqliteproviderfactory, devart.data.sqlite, version=4.6.287.0, culture=neutral, publickeytoken=09af7300eec23701" /> </dbproviderfactories> </system.data> after add below block code in app.config <?xml version="1.0"?> <configuration>   <configsections> <!-- more information on entity framework configuration, visit http://go.microsoft.com/fwlink/?linkid=237468 --> <section name="entityframework" type="system.data.entity.internal.configfile.entityframeworksection, entit...
Read more

java - Copying object fields -

-
what best way of copying classes when need have 2 independent variables? have simple class: public class myclass { boolean = false; string b= "not empty"; } do need make method : assign(myclass data ) { a= data.a; b= data.b; } is there automatic method copy (duplicate) objects in java? do need make method : pretty close. instead of making method, should make constructor. such constructors called copy constructor , , create them this: myclass(myclass data) { = data.a; b = data.b; } and create copy of instance, use constructor this: myclass obj1 = new myclass(); myclass obj2 = new myclass(obj1); copy constructor can tedious : using copy constructor create deep-copy can tedious, when class has mutable fields. in case, assignment create copy of reference, , not object itself. have create copy of fields (if want deep copy). can go recursive. a better way create deep copy serialize , deserialize object. why not use clone()? ...
Read more

c++ - Clear the memory after returning a vector in a function -

-
i have function processes , stores lot of data in , returns results vector of class. amount of data stored in function tremendous , want clear storage memory of function after finished job. necessary (does function automatically clear memory) or should clear memory function? update: vector<customers> process(char* const *filename, vector<int> id) { vector<customers> list_of_customers; (perform actions) return list_of_customers; } variables defined locally within function automatically released @ end of function scope. destructors objects called, should free memory allocated objects (if objects coded correctly). example of such object std::vector . anything you've allocated new must have corresponding delete release storage. try avoid doing own allocation , use raii instead, i.e. containers or smart pointers.
Read more