I have a code like this
int i;
for(i=0; i<n ; i++)
{
....
char* ref_error = "";
if( isSeatAvailable(&tmp, movie_name, seat_number, &ref_error) == 0)
{
printf("available %s\n", seat_number);
}
else
{
logError(ref_error);
}
....
}
If isSeatAvailable returns 0, it works perfectly, but it returns -1 and the program continues to else statement, the variables breaks down: like n becomes 4509408 etc.
The thing is,
If I re-write code like this and call isSeatAvailable method outside of if statement, it works perfect!
int i;
for(i=0; i<n ; i++)
{
....
int res = isSeatAvailable(&tmp, movie_name, seat_number, &ref_error);
if( res == 0)
{
printf("available %s\n", seat_number);
}
else
{
logError(ref_error);
}
....
}
What might cause the problem here?
Here's the method I'm calling
int isSeatAvailable(hall** halls,char* movie_name,char* seat_no, int ticket_count, char** ref_error)
{
....
sprintf(*ref_error,"Seat %s is not defined at %s.",seat_no,tmp->hall_name);
....
}
The problem is in the call to sprintf. The first parameter ref_error comes from:
char* ref_error = "";
And now sprintf tries to overwrite the constant "" with the error message. Strange things will follow!
sprintf needs a real buffer (of sufficient size) to store the message into. Not just a pointer.
Related
I'm given a task to write a program that checks a piece of code, maximum of 20 lines of code, when the program runs you type in a function name, number of lines of code and type in the codes.
It's meant to search in the code and return if the function name you entered is a Library Function or User Defined Function or No Function if it doesn't find it, the code I've written is below, it doesn't work because I made mistakes and I've been trying to fix it but can't seem to figure it out, and I tried debugging to see where I made mistake, and I figured that in the function SearchRealisation it returns an error that
Run-Time Check Failure #2 - Stack around the variable 'buff' was
corrupted.
This program sample returns Library function instead of user defined function
type the function name: addition
Get count string in code: 9
int addition(int num1, int num2)
{
int result = num1 + num2; //trial
return result;
}
int main()
{
addition(8, 9);
}
Output is Library Function but correct output should be User Defined Function since it was defined in the code
void InputText(int length, char Text[MAX_STRINGS][MAX_COLUMNS])
{
//Repeat by Count String
gets_s(Text[0]);
for (int i = 0; i < length; i++)
gets_s(Text[i]);
//Output a string (starting with � zero and ending with Count String-1)
}
void OutMesseg(int param)
{
//Display one of three messages according to the parameter
if (param == -2)
printf("%s", "user defined function");
else if (param == -1)
printf("%s", "no function");
else
printf("%s", "library function");
}
char* DeleteComentsInString(char Text[MAX_STRINGS], char New[MAX_STRINGS])
{
char* a = strstr(Text, "//");
int len = strlen(Text);
if (a != NULL) len -= strlen(a);
strncpy(New, Text, len);
New[len] = '\0';
return New;
}
bool IsTypeC(char Word[MAX_STRINGS])
{
char ctype[6][MAX_STRINGS] =
{
"int",
"bool",
"char",
"float",
"double",
"void"
};
for (int i = 0; i < 6; i++)
{
if (strstr(Word, ctype[i]) != 0)
return true;
}
return false;
}
int SearchRealisation(int length, char Text[MAX_STRINGS][MAX_COLUMNS], int index_fanc, int& end)
{
int count = 0;
int start = -1;
end = -1;
char buff[MAX_STRINGS];
//Find first {
for (int i = index_fanc + 1; i < length && !count; i++)
{
if (strstr(DeleteComentsInString(Text[i], buff), "{") != NULL)
{
count++;
start = i;
}
}
//find last }
for (int i = start + 1; i < length && count; i++)
{
if (strstr(DeleteComentsInString(Text[i], buff), "{") != NULL)
count++;
else if (strstr(DeleteComentsInString(Text[i], buff), "}") != NULL)
count--;
if (!count)
end = i;
}
if (end == -1)
start = -1;
else
return start;
}
int SearchFunction(int length, char Text[MAX_STRINGS][MAX_COLUMNS], char FunctionName[MAX_COLUMNS], int& end)
{
//bool flag = false;
char commentDel[120];
int in;
for (int i = 0; i < length; ++i)
{
DeleteComentsInString(Text[i], commentDel);
if (strstr(commentDel, FunctionName) != NULL)
{
in = strlen(commentDel) - strlen(strstr(commentDel, FunctionName));
if ((in == 0 || (in != 0 && commentDel[in - 1] == ' ')) && (commentDel[in + strlen(FunctionName)] == ' ' || commentDel[in + strlen(FunctionName)] == '(') && strstr(commentDel, ";") == NULL)
{
return SearchRealisation(length, Text, i, end);
}
}
}
end = -1;
return -1;
}
int SearchResult(int length, char Text[MAX_STRINGS][MAX_COLUMNS], char FunctionName[MAX_COLUMNS])
{
int index;
int end;
int start = SearchFunction(length, Text, FunctionName, end);
if (start == -1)
return -1;
index = SearchFunction(length, Text, FunctionName, end);
if (index < 0)
return -2;
return index;
}
int findFunction(char string[MAX_STRINGS][MAX_COLUMNS], char* functName, int M)
{
return 0;
}
int main()
{
int length = 0;
char Code[MAX_STRINGS][MAX_COLUMNS] = { 0 };
char FunctionName[MAX_COLUMNS];
//char ConstantName[MAX_STRINGS];
printf("type the function name: ");
scanf("%s", &FunctionName);
printf("Get count string in code: ");
scanf("%d", &length);
InputText(length, Code);
printf("\n");
OutMesseg(SearchResult(length, Code, FunctionName));
return 0;
}
Well, you have been given a very difficult task:
There's no way to check this, as functions are resolved by a dynamic process that depends on your filesystem state, which is not available at runtime, after you have already compiled your program.
How do you distinguish a function that is compiled in a separate (but user defined) compilation unit from a system defined function? (e.g. double log(double);) that is defined in a math library? There is no way: the linker gets both from a different place (in the first case it gets it from the place you compiled the separate module, in the system case it gets it from a common library directory that has all the system related functions), but you don't have that information available at runtime).
In order to do this task feasible, you'd at least have the full set of source code files of your program. Preprocess them with the cpp(1) preprocessor (so you bypass all the macro expansion invocations) and then check for all function calls in the source code that are not provided in the full set of sources you have. This is quite similar to what the linker does. After compilation, the compiler leaves an object file with the compiled code, and a symbol table that identifies all the unresolved identifiers, and more important all the provided identifiers from this module. The linker then goes on all your modules trying to solve the unknowns, and for each that it doesn't have a solution in your code, it goes to the library directory to search for it. If it doesn't find it in either one, it fails telling you something is wrong.
In my opinion, you have been given a trap task, as the C language preprocess its input (this is something you should do, as many functions are hidden in the internals of macro bodies), then parse the code (for this, you need to write a C parser, which is no trivial task) to select which identifiers are defined in your code and which aren't. Finally you need to check all the calls you do in the code to divide the set in two groups, calls that are defined (and implemented) in your code, and calls that aren't (implemented, all the calls the compiler needs must be defined with some kind of prototype).
It's my opinion, but you have not a simple task, solvable in a short program (of perhaps one hundred lines) but a huge one.
Thanks a lot to everyone that answered I came up with a way to search the code for function definition and thereby return a value if its defined or not, or not even found, might not be the best solution to the task but works so far
I have some functions that should allow me to manage a structure which was allocated dynamically. The allocation of the memory and the input of data in those is no real problem, though my program stops when it reaches a certain line of code: (No warning or problems detected)
if(codeV == p_vendite[ctrl_j].p_venditore[ctrl_i].codVenditore)
This line is in the function called VenditeProdotto(Vendite *p_vendite).
Here's the important part of the code (defining structures)
typedef struct _Venditore {
int codVenditore;
int codProdotto;
int qty;
} Venditore;
typedef struct _Vendite{
int mmGG;
Venditore *p_venditore;
} Vendite;
void AggiungiVendita (Vendite *p_vendite);
void VenditeProdotto(Vendite *p_vendite);
void VenditeVenditore(Vendite *p_vendite);
...
Here's main():
int main() {
int check, i, count, flag, choice;
Vendite *p_Vendite;
...
...
p_Vendite = (Vendite*) calloc(numVenditori,sizeof(Vendite));
...
...
p_Vendite->p_venditore = (Venditore*)calloc(numVenditori,sizeof(Venditore));
/*menu*/
flag = TRUE;
do{
choice = menu();
switch (choice) {
case 1 : AggiungiVendita(p_Vendite); break;
...
case 3 : VenditeProdotto(p_Vendite); break;
case 4 : VenditeVenditore(p_Vendite); break;
...
}
} while (flag == TRUE);
return 0;
}
And here are the functions:
void AggiungiVendita (Vendite *p_vendite) {
int flag, check, answer;
i = 0;
do{
/*input of struct - codVenditore,codProdotto,qty*/
...
check = scanf("%d", &(p_vendite[j].p_venditore[i].codVenditore));
...
/*input*/
check = scanf("%d", &(p_vendite[j].p_venditore[i].codProdotto) );
...
/*controllo sull'input*/
check = scanf("%d", &(p_vendite[j].p_venditore[i].qty) );
...
...
//asking to redo or quit
} while(flag == TRUE && i < numVenditori);
return;
}
int menu() {
//just a standard menu, no problem here
...
return choice;
}
void VenditeProdotto(Vendite *p_vendite) {
int check = 0, codeP = 0, ctrl_i = 0, ctrl_j = 0; //ctrl_i,ctrl_j are increasing variables and I use them to search among the structures
...//input, continues after
Where I find the debug error: (line 3 after this)
for(ctrl_j = 0; ctrl_j < numVendite; ctrl_j++) {
for(ctrl_i = 0; ctrl_i < numVenditori; ctrl_i++) {
if (codeP == p_vendite[ctrl_j].p_venditore[ctrl_i].codProdotto)
printf("\nSeller %d, quantity sold: %d in day %d", p_vendite[ctrl_j].p_venditore[ctrl_i].codVenditore, p_vendite[ctrl_j].p_venditore[ctrl_i].qty, ctrl_j+1);
else
continue;
}
}
return;
}
Basically I don't know if it's really legit to use the first line of code that I've talked about, with . instead of ->, but if I try to change the syntax I get detected errors. Any ideas?
At first I thought about something like (p_vendite+ctrl_j)->(p_venditore+ctrl_i)->codProdotto, since it's a pointer but it doesn't seem working.
There are a couple of obvious bugs:
Allocation of Vendite
You're allocating numVenditori elements for p_Vendite, but later on you are iterating numVendite times over the same pointer:
p_Vendite = (Vendite*) calloc(numVenditori,sizeof(Vendite));
...
for(ctrl_j = 0; ctrl_j < numVendite; ctrl_j++) {
for(ctrl_i = 0; ctrl_i < numVenditori; ctrl_i++) {
if (codeP == p_vendite[ctrl_j].p_venditore[ctrl_i].codProdotto)
The allocation should read:
p_Vendite = (Vendite*) calloc(numVendite,sizeof(Vendite));
or as I would prefer it:
p_Vendite = calloc (numVendite, sizeof *p_Vendite);
Allocation of Venditore
p_Vendite->p_venditore = (Venditore*)calloc(numVenditori,sizeof(Venditore));
You're only allocating the p_venditore element for one of your Vendite structs. You need to allocate all of them in a loop:
for (int j = 0; j < numVendite; j++) {
p_Vendite[j].p_venditore = (Venditore*)calloc(numVenditori,sizeof(Venditore));
// And check for allocation errors
}
i'm making a small test to see if a word is inside another, and i want to return the index where that word begins.
Example: if i check "um" inside "amolum" the return value should be 4(position of the leter "u" where the word begins.
This is what my code looks like:
(...)
int cad_look_str (char s1[], char s2[]) {
int indS1 = 0, indS2 = 0;
while (s1[indS1]!='\0'|| s2[indS2]!='\0') {
if (s1[indS1]==s2[indS2]) {
indS1++;
indS2++;
}
else indS1=0;
}
if (s2[indS2]=='\0' && s1[indS1]!='\0') return -1;
else return indS2-strlen (s1);
}
void main () {
char s[100];
char s1[100];
scanf ("%s",s);
scanf ("%s",s1);
printf ("%d \n", cad_look_str(s1,s) );
}
The problem is that when i compile this, it doesn't stop looping on scanf... It just continues to ask for strings.
If i put cad_look_str(s1,s1) on the last line, it works fine... Why is this happening?
Regards
Your initial loop condition will never terminate if the first characters don't match your comparison test within your if statement.
The 'while' loop checks to ensure the current character positions (both 0 on first pass) are non-terminators. If they're not, and they're not equal, indS1 is reset to its starting position. indS2 never changes, thus the while condition is unchanged.
Might look at some other string functions to accomplish your task unless the scanning is a mandatory component for some reason.
Index of second string should be incremented in the else part also.
if (s1[indS1]==s2[indS2])
{
indS1++; indS2++;
}
else {
indS1=0;
indS2++;
}
changed cad_look_str() for situations like s1 : gdgddadada, s2 : dadada
int cad_look_str (char s1[], char s2[]) {
int indS1 = 0, indS2 = 0;
int flag = 0;
while (s1[indS1]!='\0'&& s2[indS2]!='\0') {
if (s1[indS1]==s2[indS2]) {
indS1++;
indS2++;
flag = 1;
}
else
{
indS1=0;
indS2++;
if(flag) indS2--; // to work with srtrings s1: gdgddadada s2: dadada
flag = 0;
}
}
if (s2[indS2]=='\0' && s1[indS1]!='\0') return -1;
else return indS2-strlen (s1);
}
//Function to store select_field
void store_field(int num_fields, unsigned long *lengths,
MYSQL_ROW row, char elect_type[10][100])
{
//Storing select_field below
int i,j,k,g;
for( i=1;i < num_fields;i=i+10)
{
// i+10 so that loop is executed one time only,
// i=1 bcoz 2nd entry is select_type
for (j=0;j<lengths[i];j++)
{
if (row[i] != NULL)
{
select_type[k][j] = *row[i];
row[i]++;
}
if (row[i] == NULL)
{
select_type[k][j]= '\0';
printf ( "NULL\n");
break; // row[i] is null for fields containing NULL
}
}
for (j;j<100;j++)
{
select_type[k][j]='\0';
}
// setting every other empty field in current row
// of select_type to NULL
}
k++;
}
g = k; //HERE I AM GETTING THE ERROR
for (k;k<10;k++){for(j=0;j<100;j++)
{
select_type[k][j]='\0';
}
}
I have already declared k in the function but I am getting the error.
If you get "not in a function", that means that the code being flagged is, wait for it, not in a function.
Probably a mis-matched closing brace (}) that causes your function to end before you think it does.
I gave up on re-formatting your code to find the problem.
You've got an extra closing bracket. The line
} g=k; **//HERE I AM GETTING THE ERROR**
closes the function.
I took the liberty of formatting out the code indentation. If you maintain good indentation it should be clear that the } is out of place:
#include <stdio.h>
#include <ctype.h> // For tolower() function //
//Function to store select_field
void store_field(int num_fields,unsigned long *lengths,MYSQL_ROW row,char select_type[10][100]){
//Storing select_field below
int i,j,k,g;
for( i=1;i < num_fields;i=i+10){ // i+10 so that loop is executed one time only , i=1 bcoz 2nd entry is select_type
for (j=0;j<lengths[i];j++){
if (row[i] != NULL){ select_type[k][j] = *row[i];
row[i]++;
}
if (row[i] == NULL) { select_type[k][j]= '\0'; printf ( "NULL\n");break; // row[i] is null for fields containing NULL
}
}for (j;j<100;j++){select_type[k][j]='\0';} //setting every other empty field in current row of select_type to NULL
} k++;
// } g=k; **//HERE I AM GETTING THE ERROR**
for (k;k<10;k++){for(j=0;j<100;j++){select_type[k][j]='\0'; }}
}
You should always indent your code to avoid this kind of error. You can find different indentation styles, choose the one you like the most
http://en.wikipedia.org/wiki/Indent_style
There are also automatic indentation tools, below is your code correctly indented
void store_field(int num_fields,unsigned long *lengths,MYSQL_ROW row,char select_type[10][100])
{
int i,j,k,g;
for( i=1;i < num_fields;i=i+10)
{
for (j=0;j<lengths[i];j++)
{
if (row[i] != NULL)
{
select_type[k][j] = *row[i];
row[i]++;
}
if (row[i] == NULL)
{
select_type[k][j]= '\0';
printf ( "NULL\n");
break; // row[i] is null for fields containing NULL
}
}
for (j;j<100;j++)
{
select_type[k][j]='\0';
}
}
k++;
}
g=k; **//HERE I AM GETTING THE ERROR**
for (k;k<10;k++){for(j=0;j<100;j++)
{
select_type[k][j]='\0';
}
}
}
All the errors and extra brackets become evident immediately. Check for some code style guides, there many, choose one you like and stick to that one.
Guys so I'm working on the web service assignment and I have the server dishing out random stuff and reading the uri but now i want to have the server run a different function depending on what it reads in the uri. I understand that we can do this with function pointers but i'm not exactly sure how to read char* and assign it to a function pointer and have it invoke that function.
Example of what I'm trying to do: http://pastebin.com/FadCVH0h
I could use a switch statement i believe but wondering if there's a better way.
For such a thing, you will need a table that maps char * strings to function pointers. The program segfaults when you assign a function pointer to string because technically, a function pointer is not a string.
Note: the following program is for demonstration purpose only. No bounds checking is involved, and it contains hard-coded values and magic numbers
Now:
void print1()
{
printf("here");
}
void print2()
{
printf("Hello world");
}
struct Table {
char ptr[100];
void (*funcptr)(void)
}table[100] = {
{"here", print1},
{"hw", helloWorld}
};
int main(int argc, char *argv[])
{
int i = 0;
for(i = 0; i < 2; i++){
if(!strcmp(argv[1],table[i].ptr) { table[i].funcptr(); return 0;}
}
return 0;
}
I'm gonna give you a quite simple example, that I think, is useful to understand how good can be functions pointers in C. (If for example you would like to make a shell)
For example if you had a struct like this:
typedef struct s_function_pointer
{
char* cmp_string;
int (*function)(char* line);
} t_function_pointer;
Then, you could set up a t_function_pointer array which you'll browse:
int ls_function(char* line)
{
// do whatever you want with your ls function to parse line
return 0;
}
int echo_function(char* line)
{
// do whatever you want with your echo function to parse line
return 0;
}
void treat_input(t_function_pointer* functions, char* line)
{
int counter;
int builtin_size;
builtin_size = 0;
counter = 0;
while (functions[counter].cmp_string != NULL)
{
builtin_size = strlen(functions[counter].cmp_string);
if (strncmp(functions[counter].cmp_string, line, builtin_size) == 0)
{
if (functions[counter].function(line + builtin_size) < 0)
printf("An error has occured\n");
}
counter = counter + 1;
}
}
int main(void)
{
t_function_pointer functions[] = {{"ls", &ls_function},
{"echo", &echo_function},
{NULL, NULL}};
// Of course i'm not gonna do the input treatment part, but just guess it was here, and you'd call treat_input with each line you receive.
treat_input(functions, "ls -laR");
treat_input(functions, "echo helloworld");
return 0;
}
Hope this helps !