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8 years, 6 months ago.
Converting float value to char *array
Hello, I have a pointer array. I am trying to convert float value into char so I can store it in the array. How it is possible? I am using a way but it is not working. The compiler is building it but it is not working in real system.
This is my array -> char *zone_value[]={"0.00","0.00","0.00","0.00"," "};
float value is -> float value=0.25;
sprintf(zone_value[zone],"%f",value );
Any suggestions?
3 Answers
8 years, 6 months ago.
I'm using this for converting a single float (value) to a char array:
uint8_t *floatArray = (uint8_t *) &value; /* ftoa */
sstaub
8 years, 6 months ago.
Your original code could easily corrupt the storage space...
// zone_value is an array of pointers. // zone_value[0] points to a string with only 5 storage locations: '0', '.', '0', '0', '\0' char *zone_value[]={"1.23","4.56","7.89","0.00"," "}; // In memory as \x31, \x2E, \x32, \x33, \x00, \x34, \x2E, \x35, \x36, ... // The following sprintf could easily overrun the storage as the value // might expand to a string greater than the original storage. sprintf(zone_value[zone], "%f", value); // if value was 1.234 it would overrun the storage // In memory as \x31, \x2E, \x32, \x33, \x00, \x34, \x2E, \x35, \x36, ... // becomes \x31, \x2E, \x32, \x33, \x34, \x00, \x2E,
As an alternate, you might pre-allocate storage for the strings, and you will want to specify the formatter to control the expansion
#define MAX_LEN_FLT 10 #define NUM_ZONES 5 char * zone_value[NUM_ZONES][MAX_LEN_FLT]; // use the secure form of printf to avoid buffer overrun errors // and reserve space for the sign, in case value could be < 0 int r = snprintf(zone_value[zone], MAX_LEN_FLT, "%+5.3f", value); // "-12.345" // always a good idea to check the return code if (r < 1 || r > MAX_LEN_FLT) printf("unable to convert value to a float\n");
Is there a good reference somewhere for the "safe" forms of these commands. I don't think the textbooks I have even mention them.
posted by 25 Apr 2016Hi Oliver,
That's a great question - which might deserve its own thread of discussion. I hope others can help answer. Some libraries append _s to the functions to indicate the secure version, but this is not the "standardized" form I guess. I think C++ string functions are probably more secure (e.g. string a; a += "hello";) but for some applications I avoid these as they can cause severe memory fragmentation. I tried searching for "secure c string functions" and there are a lot of hits.
Generally, anything that writes to a buffer, should also pass the size of the buffer, so the function can avoid overrun. "strcpy" gets replaced with "strncpy" for instance.
posted by 25 Apr 20168 years, 6 months ago.
Don't know what your application is, if you want to fill a dynamic float value array, I would do this, mainly as I use something similar. But this may be a homework question.
snip-tested
float zone_value[101]; zone_value[0] = 0.00; zone_value[1] = 1.65; zone_value[2] = 0.00; zone_value[3] = 4.21; zone_value[4] = 3.68; // ........ zone_value[99] = 6.37; for(int n = 0; n < 5; n++) { sprintf(buffer,"zone value %d: = %1.2f \n",n,zone_value[n]); } sprintf(buffer,"zone value 99: = %1.2f \n",zone_value[99]);