malloc on Windows - c

Question

I'm new in this forum and i hope to do it right.
My problem is the following:
I'm writing a program that has this function:
void* s_malloc(int _size, int dim){
printf("%d %d\n", _size, dim);
char* pointer;
pointer = (char*)malloc(_size * dim);
printf("Malloc eseguita \n");
if(pointer == NULL){
ExitFailure(strerror(errno));
}else{
for(int i = 0; i < dim * _size; i++){
pointer[i] = '\0';
}
printf("Allocata\n");
return (void*)pointer;
}
return (void*) NULL;
}
I tested this function a lot ( In the truth i wrote this function a month ago and since that moment i have used it a lot ). I'm pretty sure that the function works fine.
However in this other function i use 's_malloc' and it crash
#define LDTOCAT "C:\\Users\\admin\\logdrstrace\\"
void startProcess(){
char* logfile, *logfilefullpath;
int run = TRUE, lenth = 0;
/*
for(int i = 0; i < 16; i ++){
s_malloc(60, 1);
}*/ commented
while(run){
logfile = checkLogFileDirectory();
Sleep(1000);
#ifdef DEBUG_MODE
printf("\nValue returned: %s\n", logfile);
fflush(stdout);
#endif // DEBUG_MODE
if(strcmp(logfile, NOFILEFOUND) != 0){
run = FALSE;
}
}
lenth = (strlen(LDTOCAT)+strlen(logfile)+1);
#ifdef DEBUG_MODE
printf("Let's go forward allocating memory: size %d\n", lenth);
printf("LDTOCAT size: %d, logfile size: %d + 1\n", strlen(LDTOCAT), strlen(logfile));
fflush(stdout);
#endif // DEBUG_MODE
logfilefullpath =(char*) s_malloc(lenth, sizeof(char));
#ifdef DEBUG_MODE
printf("Memory created!\n");
fflush(stdout);
#endif // DEBUG_MODE
memcpy(logfilefullpath, LDTOCAT, sizeof(LDTOCAT));
#ifdef DEBUG_MODE
printf("Created logfilefullpath with directory: %s\n", logfilefullpath);
fflush(stdout);
printf("File found: %s\n", strcat(logfilefullpath, logfile));
#endif // DEBUG_MODE
int fd = open(strcat(LDTOCAT, logfile), O_RDONLY);
if(fd <= OK){
ExitFailure(strerror(errno));
}
}
As you can see there is a for loop at the begginning commented. Now we have three possibility:
1) If i compile and run the program it fails in s_malloc function when it executes the command 'loginfulpath = (char*)s_malloc(lenth, sizeof(char))' it enters in s_malloc and crash when it calls the original malloc. Sometimes the errno varible is setted on "Not enough memory" but sometimes crashes and stop.
2) if i decomment the loop at the begginning and the stop condition is 'i<15' it crashes like in the point one
3)if i put the stop condition 'i<16', magically, it works fine.
there is a third function that opens a directory and looks for a file,
infact as you can see in the code it avoids the first 2 files found becouse
they are . and ..
#define NOFILEFOUND "Nothing"
char* checkLogFileDirectory(){
HANDLE hfile = INVALID_HANDLE_VALUE;
WIN32_FIND_DATA fdata, nullValue;
char* file = NULL;
int counter=0;
while(hfile == INVALID_HANDLE_VALUE){
hfile = FindFirstFileA(LOGDIR, &nullValue);
}
#ifdef DEBUG_MODE
printf("-FileFound: %s\n", nullValue.cFileName);
#endif // DEBUG_MODE
while(FindNextFile(hfile, &fdata) && counter != 2){
#ifdef DEBUG_MODE
printf("-File found: %s\n", fdata.cFileName);
#endif // DEBUG_MODE
if(counter == 1){
#ifdef DEBUG_MODE
printf("Third file it's my file\n");
#endif // DEBUG_MODE
file = s_malloc(strlen(fdata.cFileName), sizeof(char));
memcpy(file, fdata.cFileName, strlen(fdata.cFileName)+1);
if(file == NULL){
ExitFailure("Error reading file");
}
file[strlen(fdata.cFileName)] = '\0';
}
counter ++;
}
#ifdef DEBUG_MODE
printf("\n\=>File selected: %s", file==NULL | file == "" ? NOFILEFOUND:file);
#endif // DEBUG_MODE
return counter == 2? file : NOFILEFOUND;
}
NB: I printed the vaule of any varibles and they were correct,
I'm on Virtual machine with vmware workstation.
I'm sorry for my english i hope you will able to understand it
This is the output when it crashes in cases 1 or 2
-FileFound: .
-File found: ..
-File found: drstrace.calc.exe.00532.0000.log
Third file it's my file
32 1
Malloc eseguita
Allocata
=>File selected: drstrace.calc.exe.00532.0000.log
Value returned: drstrace.calc.exe.00532.0000.log
Let's go forward allocating memory: size 60
LDTOCAT size: 27, logfile size: 32 + 1
60 1
Malloc eseguita
Error: Not enough space!!
Thank you!!

Answer 1

Your allocation function is okay (it's a poor man's version of calloc with error checking, maybe using calloc would save some manual code and would be more efficient)
But in checkLogFileDirectory this code is wrong:
file = s_malloc(strlen(fdata.cFileName), sizeof(char));
memcpy(file, fdata.cFileName, strlen(fdata.cFileName)+1);
there's not enough space for file (nul-terminating char). You're missing 1 byte, which can corrupt the rest of your application by undefined behaviour (allocating 15 or 16 useless blocks sometimes makes it "work" because it changes the memory layout).
Why not just do:
file = strdup(fdata.cFileName);
Also, as noted in comments, if you reach a further point of your program you'll have a big issue here:
int fd = open(strcat(LDTOCAT, logfile), O_RDONLY);
LDTOCAT is a string literal, you cannot apply strcat on it. And even if you could, you wouldn't have enough room.

Answer 2

HANDLE hfile = INVALID_HANDLE_VALUE;
WIN32_FIND_DATA fdata, nullValue;
while(hfile == INVALID_HANDLE_VALUE)
{
hfile = FindFirstFileA(LOGDIR, &nullValue);
}
Note that this loop will run forever if something is wrong. Then you put the whole function in another while loop.
If the function call is valid then you have success the first time, otherwise you cannot fix a problem with brute force.
You are not closing hfile. You have many more errors in this section. There are plenty of examples and documentation for FindFirstFile you can consult.
You already have strcat, you should have strcpy too. strcpy will add null terminator at the end of the string. Just use the standard malloc and strcpy
You have to free the malloc allocation, so it's simpler if your function always returns a pointer and NULL on failure.
char* checkLogFileDirectory()
{
char* file = NULL;
WIN32_FIND_DATA fdata;
HANDLE hfile = FindFirstFile("C:\\Users\\admin\\logdrstrace\\*.log", &fdata);
if(hfile != INVALID_HANDLE_VALUE)
{
do
{
if(strcmp(fdata.cFileName, ".") == 0 || strcmp(fdata.cFileName, "..") == 0)
continue;
int len = strlen(fdata.cFileName);
file = malloc(len + 1);
strcpy(file, fdata.cFileName);
break;
} while(FindNextFile(hfile, &fdata));
FindClose(hfile);
}
return file;
}
int main()
{
char *file = checkLogFileDirectory();
if(file) {
printf("%s\n", file);
free(file);
}
return 0;
}