Does the size of an array of pointers to char matter?
Say you have
I get a runtime error "Violation Reading location 0*0000000". When I reduced the number of words in the array from 84 to 30, the program ran fine. As such, I concluded there are only a certain size you can allocate to these arrays. Further input from you guys would be much appreciated
char *words [84] = {"louie", "douie", ......"movie"}I get a runtime error "Violation Reading location 0*0000000". When I reduced the number of words in the array from 84 to 30, the program ran fine. As such, I concluded there are only a certain size you can allocate to these arrays. Further input from you guys would be much appreciated
There is a limit, due to memory size, but I don't thinks it's between 30 and 84.
How many strings are you providing in your initializer list?
If you define just 4, like
then the other 80 elements will be set to zero, which means they're null pointers.
So while words[0], words[1], words[2], words[3] are pointers to valid strings.
words[4] .. words[83] are all null pointers!
Are you trying to use any of the null pointers?
How many strings are you providing in your initializer list?
If you define just 4, like
char *words [84] = {"louie", "douie", "clouie, "movie"}; then the other 80 elements will be set to zero, which means they're null pointers.
So while words[0], words[1], words[2], words[3] are pointers to valid strings.
words[4] .. words[83] are all null pointers!
Are you trying to use any of the null pointers?
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i defined all 84, and my for loop tried to access the elements starting from position 0 all the way upto 83 when the runtime error occured. I think your reason is valid as an array is a contiguous block of memory and, as such, would quickly run out of locations. A linked list would probably be a better implementation in this case.
Try declaring the array as
Note: 'const char *' is the correct type of string literals.
const char *words[/*leave this empty*/]={/*...*/};Note: 'const char *' is the correct type of string literals.
Regarding space :
- Your array is a local variable, so it's stored on the stack
- For vc++, the default stack size is 1Mb. (which I take to be a pretty average size)
- Your array is storing pointers to string literals, which have static storage by default and are therefore not on the stack. Only the pointer are.
- The size of a char* pointer (assuming you're compiling for 32-bit) is 4 bytes.
- Hence an array of 84 char*s will take up 336 bytes
- So the array will occupy (to 2 sf) 0.032% of the available (to the stack) memory.
An array of 1Mb / 4bytes = of 262144 elements would be a different matter!
And (Assuming the = was accidentally omitted...) :
Is not valid C++ [1]
For multi-dimensional array definitions, C++ only allows one of the array dimensions to be left undefined.
does work, allocating 16 chars for each string. But the other way round (words[4][]) does not work.
If you want an array of const strings then helios const char* version is the way to go.
I suppose the 2D version could be used to a define a pre-initialized set of buffers for later use. But a vector of strings (i.e. std::vector<std::string>) would usually be used for this purpose.
(Note that if you try and change a char in one of the strings in your array, as originally defined, you will trigger an exception, as the string is stored in const memory. Allowing char* to point at const strings is an evilness to support backwards compatibility with C. New code should always use const char*)
Andy
[1] Unless it's turning up in C++0x?
- Your array is a local variable, so it's stored on the stack
- For vc++, the default stack size is 1Mb. (which I take to be a pretty average size)
- Your array is storing pointers to string literals, which have static storage by default and are therefore not on the stack. Only the pointer are.
- The size of a char* pointer (assuming you're compiling for 32-bit) is 4 bytes.
- Hence an array of 84 char*s will take up 336 bytes
- So the array will occupy (to 2 sf) 0.032% of the available (to the stack) memory.
An array of 1Mb / 4bytes = of 262144 elements would be a different matter!
And (Assuming the = was accidentally omitted...) :
char words[][] = {"louie", "douie", "clouie, "movie"}; Is not valid C++ [1]
For multi-dimensional array definitions, C++ only allows one of the array dimensions to be left undefined.
char words[][16] = {"louie", "douie", "clouie, "movie"}; does work, allocating 16 chars for each string. But the other way round (words[4][]) does not work.
If you want an array of const strings then helios const char* version is the way to go.
I suppose the 2D version could be used to a define a pre-initialized set of buffers for later use. But a vector of strings (i.e. std::vector<std::string>) would usually be used for this purpose.
(Note that if you try and change a char in one of the strings in your array, as originally defined, you will trigger an exception, as the string is stored in const memory. Allowing char* to point at const strings is an evilness to support backwards compatibility with C. New code should always use const char*)
Andy
[1] Unless it's turning up in C++0x?
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