1402 21 - COMP1002/1402 Chapter21:FunctionLibraries...

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COMP 1002/1402
Introduction to Systems Programming
Chapter 21: Function Libraries
Function Libraries
• C has several function libraries containing pre ‐
d fi d f ti defined functions we can use.
– Standard I/O (stdio.h)
– Standard library (stdlib.h)
– Type library (ctype.h)
– Math library (math.h)
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Standard Library (stdlib.h)
• Contains many of the functions we have
l d d ( ll f t ) already used (malloc, free, etc).
• Also has some very useful conversion
function:
– atof : converts a string to a double.
– atoi : converts a string to an int : converts a string to an int.
– atol : converts a string to an long.
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atoi() example
#include <stdio.h>
#include <stdlib.h>
int main() {
char str1[] = "124z3yu87";
char str2[] = "-3.4";
char *str3 = "e24";
printf("str1: %d\n", atoi (str1));
printf("str2: %d\n", atoi (str2));
printf("str3: %d\n", atoi (str3));
return 0; }
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More stdlib.h conversions
• strtod : string to double
• strtof : string to float
• strtol : string to long
• strtold : string to long double
• …
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strtod() Function
• Takes as many characters as possible that are valid
following a syntax resembling that of floating point
literals, and interprets them as a numerical value.