std :: strncmp()函数从字符比较两个以null结尾的字符串的字符不超过计数，并根据结果返回一个整数。
- 该函数有两个字符串和一个数NUM作为参数，并在两个字符串的最开始的num个字节的比较。
- num最多应等于最长字符串的长度。如果将num定义为大于字符串长度，则将进行比较，直到两个字符串的null-character(’\ 0’)为止。
- 此函数按字典顺序比较两个字符串。它从每个字符串的第一个字符开始比较。如果它们彼此相等，则继续并比较每个字符串的下一个字符，依此类推。
- 比较过程将一直终止，直到达到一个终止字符串或两个字符串中的num个字符为止。
句法 ：
int strncmp(const char *str1, const char *str2, size_t count);
Parameters:
str1 and str2: C string to be compared.
count: Maximum number of characters to compare.
size_t is an unsigned integral type.
Return Value:
Value Meaning
Less than zero str1 is less than str2.
Zero str1 is equal to str2.
Greater than zero str1 is greater than str2.
如果两个字符串的字符数均少于count，则在遇到第一个null时比较结束。
strcmp()返回什么?
strncmp()函数根据比较结果返回三种不同类型的整数值：
1.大于零(> 0)：一个正的值被返回，如果str1和STR2的字符不前num个字符相匹配，并且str1字符的ASCII值大于STR2字符的ASCII值。结果，我们可以说str1在字典上大于str2 。
// C, C++ program to demonstrate
// functionality of strncmp()
#include
#include
int main()
{
// Take any two strings
char str1[10] = "aksh";
char str2[10] = "akash";
// Compare strings using strncmp()
int result = strncmp(str1, str2, 4);
if (result == 0) {
// num is the 3rd parameter of strncmp() function
printf("str1 is equal to str2 upto num characters\n");
}
else if (result > 0)
printf("str1 is greater than str2\n");
else
printf("str2 is greater than str1\n");
printf("Value returned by strncmp() is: %d", result);
return 0;
}
输出：
str1 is greater than str2
Value returned by strncmp() is: 18
2.小于零(<0)：返回一个负值，如果str1和STR2的字符不前num个字符相匹配，并且str1字符的ASCII值大于STR2字符的ASCII值较小。结果，我们可以说str2在字典上大于str1 。
// C, C++ program to demonstrate
// functionality of strncmp()
#include
#include
int main()
{
// Take any two strings
char str1[10] = "akash";
char str2[10] = "aksh";
// Compare strings using strncmp()
int result = strncmp(str1, str2, 4);
if (result == 0) {
// num is the 3rd parameter of strncmp() function
printf("str1 is equal to str2 upto num characters\n");
}
else if (result > 0)
printf("str1 is greater than str2\n");
else
printf("str2 is greater than str1\n");
printf("Value returned by strncmp() is: %d", result);
return 0;
}
输出：
str2 is greater than str1
Value returned by strncmp() is: -18
3.等于零(0)：该函数返回零如果与STR2高达num个字符的字符STR1匹配的字符。结果，我们不能说str1等于str2 ，直到num等于任一字符串的长度。
// C, C++ program to demonstrate
// functionality of strncmp()
#include
#include
int main()
{
// Take any two strings
char str1[10] = "akash";
char str2[10] = "akas";
// Compare strings using strncmp()
int result = strncmp(str1, str2, 4);
if (result == 0) {
// num is the 3rd parameter of strncmp() function
printf("str1 is equal to str2 upto num characters\n");
}
else if (result > 0)
printf("str1 is greater than str2\n");
else
printf("str2 is greater than str1\n");
printf("Value returned by strncmp() is: %d", result);
return 0;
}
输出：
str1 is equal to str2 upto num characters
Value returned by strncmp() is: 0
注意：如果字符串不同，则在两种情况下，strncmp()函数返回的值都是str1和str2中第一个不匹配字符的ASCII值之间的差。
更多例子
范例1：
// CPP program to illustrate strncmp()
#include
#include
void display(char* abc, char* xyz, int res, int count)
{
if (res > 0)
std::cout << xyz << " come-before " << abc;
else if (res < 0)
std::cout << abc << " come-before " << xyz;
else
std::cout << "First " << count << " characters of string "
<< abc << " and " << xyz << " are same";
}
int main()
{
char abc[] = "GeeksforGeeks";
char xyz[] = "Geeks";
int res;
res = std::strncmp(abc, xyz, 4);
display(abc, xyz, res, 4);
return 0;
}
输出：
First 4 characters of string GeeksforGeeks and Geeks are same
范例2：
// CPP program to illustrate strncmp()
#include
#include
void display(char* abc, char* xyz, int res, int count)
{
if (res > 0)
std::cout << xyz << " come-before " << abc;
else if (res < 0)
std::cout << abc << " come-before " << xyz;
else
std::cout << "First " << count << " characters of string " <<
abc << " and " << xyz << " are same";
;
}
int main()
{
char abc[] = "GeeksforGeeks";
char xyz[] = "Geeks";
int res;
res = std::strncmp(abc, xyz, 6);
display(abc, xyz, res, 6);
return 0;
}
输出：
Geeks come-before GeeksforGeeks
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