Convert function to read from string instead of file in C
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I've been tasked with updating a function which currently reads in a configuration file from disk and populates a structure:
static int LoadFromFile(FILE *Stream, ConfigStructure *cs)
{
int tempInt;...
if ( fscanf( Stream, "Version: %d\n",&tempInt) != 1 )
{
printf("Unable to read version number\n");
return 0;
}
cs->Version = tempInt;
...}
to one which allows us to bypass writing the configuration to disk and instead pass it directly in memory, roughly equivalent to this:
static int LoadFromString(char *Stream, ConfigStructure *cs)
A couple of things to note: • The current LoadFromFile function is incredibly dense and complex, reading dozens of versions of the config file in a backward-compatible manner, which makes duplication of the overall logic quite a pain. • The functions that generate the config file and those that read it originate in totally different parts of the old system and therefore don't share any data structures so I can't pass those directly. I could potentially write a wrapper, but again, it would need to handle any structure passed in a backward-compatible manner. • I'm tempted to just pass the file as is in as a string (as in the prototype above) and convert all the fscanf's to sscanf's but then I have to handle incrementing the pointer along (and potentially dealing with buffer overrun errors) manually. • This has to remain in C, so no C++ functionality like streams can help here Am I missing a superior choice? Is there a good method for making a FILE * that simply focuses to an area in memory rather than on a disk? Any pointers, ideas or other assistance is enormously valuable.
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I've been tasked with updating a function which currently reads in a configuration file from disk and populates a structure:
static int LoadFromFile(FILE *Stream, ConfigStructure *cs)
{
int tempInt;...
if ( fscanf( Stream, "Version: %d\n",&tempInt) != 1 )
{
printf("Unable to read version number\n");
return 0;
}
cs->Version = tempInt;
...}
to one which allows us to bypass writing the configuration to disk and instead pass it directly in memory, roughly equivalent to this:
static int LoadFromString(char *Stream, ConfigStructure *cs)
A couple of things to note: • The current LoadFromFile function is incredibly dense and complex, reading dozens of versions of the config file in a backward-compatible manner, which makes duplication of the overall logic quite a pain. • The functions that generate the config file and those that read it originate in totally different parts of the old system and therefore don't share any data structures so I can't pass those directly. I could potentially write a wrapper, but again, it would need to handle any structure passed in a backward-compatible manner. • I'm tempted to just pass the file as is in as a string (as in the prototype above) and convert all the fscanf's to sscanf's but then I have to handle incrementing the pointer along (and potentially dealing with buffer overrun errors) manually. • This has to remain in C, so no C++ functionality like streams can help here Am I missing a superior choice? Is there a good method for making a FILE * that simply focuses to an area in memory rather than on a disk? Any pointers, ideas or other assistance is enormously valuable.
If you are working on Linux, fmemopen[^] is your friend. There is no equivalent function under Windows but there are some emulation projects GitHub - Snaipe/fmem: A cross-platform library for opening memory-backed libc streams.[^]. Never tried it so I don’t know how well it works.
Mircea
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I've been tasked with updating a function which currently reads in a configuration file from disk and populates a structure:
static int LoadFromFile(FILE *Stream, ConfigStructure *cs)
{
int tempInt;...
if ( fscanf( Stream, "Version: %d\n",&tempInt) != 1 )
{
printf("Unable to read version number\n");
return 0;
}
cs->Version = tempInt;
...}
to one which allows us to bypass writing the configuration to disk and instead pass it directly in memory, roughly equivalent to this:
static int LoadFromString(char *Stream, ConfigStructure *cs)
A couple of things to note: • The current LoadFromFile function is incredibly dense and complex, reading dozens of versions of the config file in a backward-compatible manner, which makes duplication of the overall logic quite a pain. • The functions that generate the config file and those that read it originate in totally different parts of the old system and therefore don't share any data structures so I can't pass those directly. I could potentially write a wrapper, but again, it would need to handle any structure passed in a backward-compatible manner. • I'm tempted to just pass the file as is in as a string (as in the prototype above) and convert all the fscanf's to sscanf's but then I have to handle incrementing the pointer along (and potentially dealing with buffer overrun errors) manually. • This has to remain in C, so no C++ functionality like streams can help here Am I missing a superior choice? Is there a good method for making a FILE * that simply focuses to an area in memory rather than on a disk? Any pointers, ideas or other assistance is enormously valuable.
-
I've been tasked with updating a function which currently reads in a configuration file from disk and populates a structure:
static int LoadFromFile(FILE *Stream, ConfigStructure *cs)
{
int tempInt;...
if ( fscanf( Stream, "Version: %d\n",&tempInt) != 1 )
{
printf("Unable to read version number\n");
return 0;
}
cs->Version = tempInt;
...}
to one which allows us to bypass writing the configuration to disk and instead pass it directly in memory, roughly equivalent to this:
static int LoadFromString(char *Stream, ConfigStructure *cs)
A couple of things to note: • The current LoadFromFile function is incredibly dense and complex, reading dozens of versions of the config file in a backward-compatible manner, which makes duplication of the overall logic quite a pain. • The functions that generate the config file and those that read it originate in totally different parts of the old system and therefore don't share any data structures so I can't pass those directly. I could potentially write a wrapper, but again, it would need to handle any structure passed in a backward-compatible manner. • I'm tempted to just pass the file as is in as a string (as in the prototype above) and convert all the fscanf's to sscanf's but then I have to handle incrementing the pointer along (and potentially dealing with buffer overrun errors) manually. • This has to remain in C, so no C++ functionality like streams can help here Am I missing a superior choice? Is there a good method for making a FILE * that simply focuses to an area in memory rather than on a disk? Any pointers, ideas or other assistance is enormously valuable.
sahil Ranka wrote:
Is there a good method for making a FILE * that simply focuses to an area in memory rather than on a disk?
Is
mmap()of any value here?"One man's wage rise is another man's price increase." - Harold Wilson
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