Objective

Implement a function that converts the start of a string into a signed long for a chosen base, then writes back the address of the first character it could not convert.

Steps

• Skip any leading whitespace, then consume an optional + or - sign.
• For base 16 (or base 0), skip an optional 0x / 0X prefix when a valid hex digit follows it.
• When base is 0, auto-detect: a 0x prefix means base 16, a leading 0 means base 8, otherwise base 10.
• Read digits valid for the base (0-9, then a-z / A-Z for values 10 and up) and build the value, applying the sign at the end.
• If endptr is not NULL, set *endptr to the first character you did not convert. When nothing was converted, leave *endptr equal to str and return 0.
• Do not worry about overflow: assume every test input fits in a long.

Objective

Implement a function that converts the start of a string into a signed long for a chosen base, then writes back the address of the first character it could not convert.

Steps

• Skip any leading whitespace, then consume an optional + or - sign.
• For base 16 (or base 0), skip an optional 0x / 0X prefix when a valid hex digit follows it.
• When base is 0, auto-detect: a 0x prefix means base 16, a leading 0 means base 8, otherwise base 10.
• Read digits valid for the base (0-9, then a-z / A-Z for values 10 and up) and build the value, applying the sign at the end.
• If endptr is not NULL, set *endptr to the first character you did not convert. When nothing was converted, leave *endptr equal to str and return 0.
• Do not worry about overflow: assume every test input fits in a long.