Christian S Christian S - 1 year ago 55
C Question

C program won't compile when GCC is called by makefile - Works otherwise

So I have a program here, that works perfectly when called with

$ gcc test.c -o test -std=c99

But when called in a makefile:

all: test

test: test.c
gcc test.c -o test -std=c99

it produces some warnings instead and gives a segmentation fault.

terminal output:

gcc -g test.c -o tester -std=c99
test.c: In function ‘test_split’:
test.c:43:2: warning: implicit declaration of function‘strdup[-Wimplicit-function-declaration]
char *str_cpy = strdup(str); // Allow mutation of original string
test.c:43:18: warning: initialization makes pointer from integer without a cast [enabled by default]
char *str_cpy = strdup(str); // Allow mutation of original string

Above error does not appear otherwise and does not produse a segmentation fault.

The code segment that fails is here. string.h is included in header.
The file is just a large file to test other functions.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdarg.h>

#define CNRM "\x1b[0m"
#define CRED "\x1b[31m"
#define CGRN "\x1b[32m"

int stringsum(char *s);
void stringsum2(char *s, int *res);
int distance_between(char *s, char c);
char *string_between(char *s, char c);
char **split(char *s);

static int test_num = 1;

static void logger(int passed, char *s)
char *res;
char *color;

if (passed) {
res = "PASS";
color = CGRN;
} else {
res = "FAIL";
color = CRED;
printf("[Test %d][%s%s%s] %s\n", test_num++, color, res, CNRM, s);

static void test_split(char *str, char **correct)
int i, pass = 1;
char buf[512] = { 0 };
char *str_cpy = strdup(str); // Allow mutation of original string
char **res = split(str_cpy);

if (!res || !res[0]) {
pass = 0;
sprintf(buf, "split() returned NULL or an empty array");
goto end;

for (i = 0; correct[i]; i++) {
if (!res[i]) {
pass = 0;
sprintf(buf, "split() returned fewer words than expected");
goto end;

if (res[i]) {
pass = 0;
sprintf(buf, "split() returned more words than expected");
goto end;

sprintf(buf, "\n%-16s%-16s\n", "Returned", "Expected");

for (i = 0; res[i]; i++) {
char tmp[256] = { 0 };
sprintf(tmp, "%-16s%-16s\n", res[i], correct[i]);
strcat(buf, tmp);
if (strcmp(res[i], correct[i])) {
pass = 0;
goto end;

logger(pass, buf);

static void test_stringsum(char *input, int expected)
int test;
char buf[256] = { 0 };

test = stringsum(input);
sprintf(buf, "Returned: %d, Expected: %d", test, expected);
logger(test == expected, buf);

static void test_distance_between(char *str, char c, int expected)
int test;
char buf[256] = { 0 };

test = distance_between(str, c);
sprintf(buf, "Returned: %d, Expected: %d", test, expected);
logger(test == expected, buf);

static void test_string_between(char *str, char c, const char *expected)
char *res_char;
char buf[256] = { 0 };

res_char = string_between(str, c);
snprintf(buf, sizeof(buf), "Returned: %s, Expected: %s", res_char, expected);

if (!res_char && expected) {
logger(0, buf);
} else {
if (!expected)
logger(!res_char, buf);
logger(!strcmp(res_char, expected), buf);

static void test_stringsum2(char *input, int expected)
int res_int;
char buf[256] = { 0 };

stringsum2(input, &res_int);
sprintf(buf, "Returned: %d, Expected: %d", res_int, expected);
logger(res_int == expected, buf);

int main(void)
printf("Testing stringsum()\n");
test_stringsum("abcd", 10);
test_stringsum("a!", -1);
test_stringsum("aAzZ", 54);
test_stringsum("ababcDcabcddAbcDaBcabcABCddabCddabcabcddABCabcDd", 120);
test_stringsum("", 0);

test_num = 1;
printf("\nTesting distance_between()\n");
test_distance_between("a1234a", 'a', 5);
test_distance_between("a1234", 'a', -1);
test_distance_between("123456a12334a123a", 'a', 6);
test_distance_between("", 'a', -1);

test_num = 1;
printf("\nTesting string_between()\n");
test_string_between("a1234a", 'a', "1234");
test_string_between("a1234", 'a', NULL);
test_string_between("A123adette er svaretaasd2qd3asd12", 'a', "dette er sv");
test_string_between("", 'a', NULL);

test_num = 1;
printf("\nTesting stringsum2()\n");
test_stringsum2("abcd", 10);
test_stringsum2("abcd!", -1);
test_stringsum2("bbbdbbbbbdbbdbbbbbddbbbbbdbbdbbbbdbd", 90);
test_stringsum2("", 0);

test_num = 1;
printf("\nTesting split()\n");
test_split("abcd", (char *[]){ "abcd", NULL });
test_split("Hei du", (char *[]){ "Hei", "du", NULL });
test_split("Dette er mange ord", (char *[]){ "Dette", "er", "mange", "ord", NULL });
return 0;

Any ideas?

Edit: Added full code.

Answer Source

If you ask gcc for C99 compliant code, it will do as you asked and forget it ever knew about strdup()- This function is not covered by the C99 standard, but is rather POSIX only, so strdup is nowhere in a header file in C99 mode.

As your code doesn't see the prototype for that reason, and doesn't know strdup () will return a pointer but rather assumes an integer, it might do all sorts of havoc when 32-/64- mixed mode code where (sizeof(int) != sizeof(char*)) is generated.

Simple remedy: Don't try to use strdup in c99 mode.

Why you seem to see the bug when compiling using make and not otherwise, is something we cannot deduct from the information you have provided. I guess for some reason you aren't switching gcc into c99 mode when using the command line.

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